accidents; may be propagated both by sporules produced in proper seedvessels, by germs and otherwise.

But besides this beautiful law, the action of which may be distinctly recognised, preserving the species of organised beings in existence, notwithstanding the perpetual destruction which they wage against each other; we are able to observe the traces of another no less beautiful, that, in proportion as a species is useful in the economy of nature, so are the developement and ef ficiency of the organs and functions that effect its diffusion.

This might be inferred a priori, from what we know of the attributes of the Creator, and the analogy of his works. This, however, is a mode of reasoning not admitted in Natural History, in which a law must only be framed, as a generalised statement of a number of observed phenomena, tending to a common purpose. But that such a law exists we observe many traces of evidence. Thus there is no tribe of plants more eminently useful in the economy of nature than the grasses, the foliage and seeds of which supply the first necessaries of life, not only to man but to a multitude of the inferior animals. And, perhaps, in no tribe equally highly organised, do we observe the same tenacity of life, or the same economy and care in the reproductive organs, to avoid the introduction of parts that might be easily injured, and so prevent a successful fructification.

In the grasses, the delicate coloured flower that gives so much beauty to most other tribes, is replaced by concave husks, which are not only most hardy, but so situated that the weather can scarcely penetrate to injure the essential organs within. Besides this, the peculiar structure of the embryo, which admits of a number of stems from one seed, might be mentioned, the copious albumen, &c. But I proceed to describe, and a few words will suffice, the beautiful structure of the awn exhibited in a species of this family, which effects the introduction of the seed into the soil so wonderfully, that I cannot satisfy myself with admiration.

The Stipa pennata is a most elegant species of grass, which, though not a native of Scotland, thrives luxuriantly in the open border. Its seed is closely invested by the glumaceous perianth, which consists of two husks, a larger and a smaller, the former of which overlapse ofges of the latter, and almost entirely

envelopes it. Thus the strong outer covering of the seed is produced below into a very sharp rigid spine; and terminated above by a long awn, which is articulated to its summit. Originating near the base, and proceeding up certain ridges on this the investing valve chiefly, are lines of stiff hairs pointing upwards. The awn, when fully developed, is about thirty times the length of the seed, or about fourteen inches. It is round, tapering and plumose, with the exception of about three inches at the base, which are compressed, longitudinally sulcated, and without hairs.

The seed, therefore, and its appendages, possess a structure such as is imitated in a barbed and feathered arrow, which is so well calculated to find its way into the ground in a vertical direction. Many seeds, however, possess a similar structure, and it is not this which gives to the awn of the stipa its most striking peculiarity. It is a change which takes place upon the awn, after it has left the plant that produced it. When it has fallen from the parent plant, it enters the soil vertically, and in a few hours the base and sulcated part of the awn becomes twisted, and the feathered portion becomes horizontal. In consequence of which, it is blown round by the autumn winds like a vane, and every turn screws it farther down into the earth; for the hollows and ridges which, when it remained upon the plant, were only longitudinal sulci, have now given rise to the hollows and elevations, in a word, to the threads of a screw. Thus it is moved down, and whatever is gained, is prevented from being undone by a reverse motion of the vane, in consequence of the stiff hairs upon the glume which act as barbs.

When it has been thus worked down into the moist soil, into the situation most favourable for germinating, the attachment between the awn and seed is dissolved; for having drawn up many when they were in this condition, I have invariably procured the awn only, and never, by any chance, the seed. Such appears to be the function of the "spiral articulated deciduous awn" of this interesting species *.

*The seeds of the Stipe often occasion great inconvenience and trouble to travellers, and even to the domestic cattle of the districts where they grow. This fact is well stated in the following notice by Mr Raspail.-ED.

"On the morbid accidents to which animals are exposed by the seeds of Stipa pennata and capillata.-It is known that the husks genus Stipa terminate

The accompanying drawing represents the seed and its appendages, more or less magnified.

Explanation of the Figures in Plate I.

Fig. 6. The two valves of the glumaceous perianth, with the stiff hairs, the spine and articulated awn.

7. The grain, with part of the skin torn at the base, to shew the albumen, of which nearly the whole is composed, the cotyledon and the embryo.

8. The seed, with a fourth part of the awn, to shew its form when ready to separate from the spike.

9. The same, as it appears some hours after separation.

"

Account of the Observations and Experiments made on the Diurnal Variation and Intensity of the Magnetic Needle, by Captain Parry, Lieutenant Foster, and Lieutenant Ross, in Captain Parry's Third Voyage, with Remarks and Illustrations. By PETER Barlow, F. R. S. Mem. of the Imperial Academy of St Petersburgh, &c. (With a Plate.) Communicated by the Author.

As

S the experiments referred to in the head of this article were performed under such extraordinary advantages of locality, of

at the base in a reversed cone, which is very sharp, and covered with stiff hairs directed upwards, so that when the point penetrates into any substance, the hairs not only prevent it from coming out, but contribute to make it go deeper. M. Desfontaines, in his Flora Atlantica, and M. Lamarck in the Encyclopedie, have pointed out the inconveniences to which a seed so organised sub'jects travellers passing over the fields of Barbary, Greece, and Portugal, at the time of ripening of the stipas. The seed penetrates into their clothes, and sooner or latter disconveniences them in a high degree, by producing scratches of various depths upon the skin. A great mortality of the cattle, which took place in 1823, in the neighbourhood of the village, of Berczel in Hungary, afforded an opportunity to the Professors of the Royal University of Pesth, of making known’a still more singular effect produced by these seeds. It was found that the seeds of the stipas, which abound in the pasture grounds of Berczel, stuck to the wool of the sheep, penetrated into the skin, and even made their way to the internal organs. On dissecting a great number of these sheep, seeds were found in the vicinity of the liver and in the peritonæum, and the skinyamined between the eye and the light, had the appearance of Lave alread. As these grasses occur in all the southof Decem

instruments, and of observers, they cannot fail to be highly interesting to every one who has paid attention to this curious and important branch of natural philosophy. With regard to locality, no place could have been more admirably situated than Port Bowen, in latitude 73° 14' N., longitude 88° 54′ W., with a dip of 88° 1′, and consequently within a very short distance of the magnetic pole, and yet sufficiently remote to leave to the needles a natural directive power, which they would in all probability have lost, had the approximation to the Pole been much greater. With regard to instruments, every thing that could be effected by the skill of the most distinguished artists in London, was liberally supplied to the expedition by the Government; and as observers, it is sufficient to mention only the names of Parry and Foster, as they cannot fail to inspire us with every possible confidence, both with respect to the accuracy of the observations, and to the most careful and unbiassed registry of the results. It is but fair, however, to state, that these two distinguished individuals alone, would not have been able, with all the zeal they are known to possess, to have obtained such a series of results as those to which we are now referring. It was necessary for this that they should be seconded by the cordial assistance and co-operation of the other officers of the expedition. This assistance was cheerfully given; and it is acknowledged in the most handsome and liberal terms by the authors of the memoir in which these experiments are recorded, and which has been recently published as a separate part of the Transactions of the Royal Society for 1826.

The experiments commenced about the 10th of December 1824, and were continued to the end of May 1825; and, when we consider that, for a considerable part of this time, the sun was below the horizon,-that the thermometer was sometimes 40° below zero,-that the place of observation, a snow house,

ern parts of Europe, the above fact ought to fix the attention of the agriculturists of those countries. The stipe do not furnish good fodder, and the meadows would lose nothing by their absence. If they could not be extirpated all at once, the flowers are surmounted by.an awn upwards of a foot long, by which they might easily be plucked off, before detaching themselves spontaneously. Should a seed happen to have buried itself in the substance of the skin, it would require to be extracted to ordinary means, for accidents husks of this kind are not to be remedied by a mbe 'treatment."

was at a distance from the ships, in order that the needles should be out of the influence of the iron on board; and that, notwithstanding these obstacles, the needles were carefully watched, the experiments performed, and the results carefully registered every hour, and frequently oftener, during this whole period; we shall feel convinced, that more than common exertions were made, and more than usual interest must have been excited, in the pursuit of these curious and valuable experiments; and, if we add to this, that these energies and these means were employed in a situation where Nature has placed her great depot of magnetic powers, and where every phenomenon of this kind is exhibited on the grandest scale, we shall then, and not till then, sufficiently appreciate the value of these interesting and important results.

With this feeling, I have thought that a brief abstract of these experiments would be acceptable to many of the readers of the Edinburgh Journal, particularly to those who have not the opportunity of consulting the original memoir; and I have accordingly, in the following pages, endeavoured to convey within the least compass, a general view of the subject, and have ventured also upon one or two illustrations of some of the theoretical points touched upon by the authors of the papers in question.

The first of the magnetic articles is by Lieutenant Foster, from which it appears, that, previous to his leaving England, he had determined upon making a series of observations on the daily variation of the magnetic needle, when any opportunity offered of so doing; and the first occurred at Whale Fish Islands, during the time of trans-shipping the stores from the transport which had accompanied the expedition to that place. The time employed in these experiments was only three days, consequently the results are not so certain as we could wish; but it is satisfactory to find, that the few facts which were obtained agree remarkably well with each other, both as to quantity and to the time of the day when the variation was the greatest westerly, the least westerly variation, or the maximum of easterly variation, occurred during the night, and was not observed. The greatest daily variation westerly was 23', and this occurred at 1h 10′ r. M., at which time the sun was west by compass, the mean variation being 70° 2′ W., and dip 82° 53′ W. The important remark, distinguished above by italics, seems to have been a strong incitement to Lieutenant Foster to prosecute the subject again on a larger scale the next favourable opportunity, which did not occur till the ships were laid up for the winter at Port Bowen. At this place, as we have already stated, the experiments were begun on the 10th of December 1824, on one needle only. In the