July 15, 1875] 



NATURE 



209 



as astonishing to everyone else as they were to Mr. 

 Darwin himself. From a most carefully conducted series 

 of experiments from which every possible source of error 

 seems to have been eliminated, it appears that the absorp- 

 tion by a gland of „.,s\nj, of a grain of carbonate of am- 

 monia (this salt producing no effect when absorbed 

 through the root) is sufficient to excite inflection and 

 aggregation of the protoplasm. With nitrate of ammonia 

 a similar effect is produced by the ^j,';,^ of a grain ; while 

 the incredibly small quantity of ^^,irir,r.js of ^ grain of phos- 

 phate of ammonia produces a like effect. Mr. Darwin 

 believes that carbonate of ammonia is also absorbed in 

 the gaseous state by the tentacles ; but we venture to 

 think that the evidence on this point is not conclusive. 

 In both the experiments which he records the air sur- 

 rounding the plant was more or less humid, and the effect 

 was much more intense in the one where the air was the 

 dampest, indicating apparently that the inflection was 

 due to the absorption of the extremely soluble gas by the 

 moisture which was in contact with the ^tentacles. This 

 would also afford an explanation of what he regards as " a 

 curious fact, that some of the closely adjoining tentacles 

 on the same leaf were much, and some apparently not in 

 the least, affected," if we suppose that they were clothed 

 with larger and smaller amounts of moisture. The view 

 that the glands have no power of absorbing gases or 

 effluvia receives confirmation 'from the failure of the 

 attempt to induce inflection or aggregation by the affixing 

 of particles of meat in close proximity to the tentacles, 

 but without actual contact. 



We cannot follow Mr. Darwin through his exhaustive 

 series of experiments on the effects of various solutions 

 of mineral salts, acids, and poisons, on the leaves of 

 Drosera. With organic fluids the aggregation of the pro- 

 toplasm and inflection of the tentacles furnish a most 

 delicate and unerring test of the presence of nitrogen. 

 The effect of inorganic salts and poisons can by no 

 means be inferred from the effect of the same substances 

 on living animals, nor from their chemical affinity. Nine 

 salts of sodium all produced inflection, and were not 

 poisonous except when given in large doses ; while seven 

 of the corresponding salts of potassium did not cause 

 inflection, and some of these were poisonous. This cor- 

 responds to the statement of Dr. Burdon Sanderson, 

 that sodium salts may be introduced in large quantities 

 into the circulation of mammals without any injurious 

 effects, whilst small doses of potassium salts cause 

 death by suddenly arresting the movements of the 

 heart. Benzoic acid, even when so weak as to be scarcely 

 acid to the taste, acts with great rapidity and is highly 

 poisonous to Drosera, although it is without marked effect 

 on the animal economy. The poison of the cobra, on the 

 other hand, so deadly to all animals, is not at all poisonous 

 to Drosera, although it causes strong and rapid inflection 

 of the tentacles, and soon discharges all colour from the 

 glands. 



The last point of investigation is the mode of transmis- 

 sion and nature of the conducting tissue of the motor 

 impulse from one tentacle to another. It has been already 

 stated that the seat of irritability is limited to the glands 

 themselves and a few of the uppermost cells of the 

 pedicels, the blade of the leaf itself not being sensitive to 

 any stimulant. In order to be conveyed from one ten- 



tacle to another, the impulse has therefore to be trans- 

 mitted down nearly the whole length of the pedicel ; and 

 it appears to be conveyed from any single gland or small 

 group of glands through the blade to the other tentacles 

 more readily and effectually in a longitudinal than in a 

 transverse direction. It can be shown that impulses 

 proceeding from a number of glands strengthen one 

 another, spread further, and act on a larger number of 

 tentacles than the impulse from any single gland. The 

 phenomenon already alluded to, of the aggregation 

 of the protoplasm in a tentacle incited indirectly by 

 the irritation of other glands on the leaf— this aggre- 

 gation advancing not upwards, but downwards, in each 

 tentacle — is spoken of by Mr. Darwin as partaking 

 of the nature of those actions which in the nervous 

 systems of animals are called reflex. The existence 

 of such a phenomenon— of which this is the only 

 known instance in the vegetable kingdom— is one of the 

 most extraordinary points brought out by these investi- 

 gations. It will be recollected that the transmission of 

 the motor impulse in the sensitive leaves of Mimosa is in 

 a precisely opposite direction, travelling upwards from 

 the base to the apex of those pinnas which are indirectly 

 irritated in consequence of the direct irritation of other 

 pinnse of the same leaf. The arrangement and direction 

 of the fibro-vascular bundles in the leaves of Drosera are 

 shown in Fig. 4 ; and Mr. Darwin's inquiries were first 

 directed to solve the question whether the impulse was 

 conveyed through the vascular system ; but he came to the 

 conclusion that it is not sent, at least exclusively, through 

 the spiral vessels or through the tissue immediately sur- 

 rounding them. He believes, on the contrary, that the 

 conducting tissue is the parenchyma or cellular tissue of 

 the mcsophyll of the leaf ; and that it is chiefly delayed by 

 the obstruction offered by the cell-walls through which it 

 has to pass ; the transmission of the impulse being indi- 

 cated by the phenomenon of aggregation of the proto- 

 plasm, which is transmitted gradually from cell to cell. 



A few other species of Drosera were examined, but 

 presented no special phenomena of interest ; and the 

 remainder of the volume is occupied by the narrative of 

 researches on other carnivorous plants, a review of which 

 we must defer to a future number. 



Alfred W. Bennett 

 {To be continued^ 



PERCY'S METALLURGY 

 Metallurgy : Introduction, Refractory Materials ana 

 Fuel. By John Percy, M.D., F.R.S. (London: 

 J. Murray, 1875). 



THIS valuable work is not merely a new edition of 

 the volume previously published by its distinguished 

 author, for it contains more than 350 pages of fresh 

 matter, and several articles on subjects which were not 

 treated of originally. Dr. Percy's "Metallurgy" is so 

 well known as the standard book in this country that it 

 may be well to indicate as succinctly as possible the 

 differences between the present volume and the portion 

 of the one published in i86r, which was devoted to refrac- 

 tory materials and fuel. 

 Much information has been added to the section which 



