MICROSCOPIC STUDY OF FLOWERING PLANTS. '41 



prosecuted in this direction, may be mentioned the discovery, 

 that the movement of " rotation" of the protoplasma (or the viscid 

 granular fluid at the expense of which the nutritive act seems to 

 take place) vs^ithin the cells, which was first observed by the 

 Abbe Corti in the Qhara in 1776, is by no means a unique or 

 exceptional case ; for that it may be detected in so large a num- 

 ber of instances, among Phanerogamia no less than among Cryp- 

 togamia, as apparently to justify the conclusion that it takes 

 place in Vegetable cells generally, at some period or other of 

 their evolution. In studying the phenomena of Vegetable '^n- 

 trition, the Microscope has been most effectually applied, not 

 merely to the determination of changes in the form and arrange- 

 ment of the elementaiy parts, but also to the detection of such 

 changes in their composition, as ordinary Chemistry would be 

 quite at fault to discover ; each individual cell being (so to speak) 

 a laboratory' in itself, within which a transformation of organic 

 compoitnds is continually taking place, not only for its own 

 requirements, but for those of the economy at large; and these 

 changes being at once made apparent by the application of 

 chemical reagents to microscopic specimens whilst actually under 

 observation. Hence the Vegetable Physiologist finds, in this 

 Microscopic Chemistry, one of his most valuable means of tracing 

 the succession of the changes in which Nutrition consists, as 

 well as of establishing the chemical nature of particles far too 

 minute to be analyzed in the ordinary way ; and he derives 

 further assistance in the same kind of investigation, from the 

 application of Polarized Light (§ 63), which immediately enables 

 him to detect the presence of mineral deposits, of starch-granules, 

 and of certain other substances which are peculiarly affected by 

 it. One of the most interesting among the general results of 

 such researches, has been the discovery that the true cell-wall of 

 the Plant (the " primordial utricle" of Mohl) has the same albumi- 

 nous composition as that of the Animal ; the external cellulose 

 envelope, which had been previously considered as the distinc- 

 tive attribute of the Vegetable -cell, being in reality but a secre- 

 tion from its surface. Of all the applications of the Microscope, 

 however, to the study of the life-history of the Flowering plant, 

 there is none which has excited so much interest, or given rise 

 to so much discussion, as the nature of the process by which the 

 Ovule is fecundated by the penetration of the pollen-tube. This 

 question, in the opinion of the author, may be considered as now 

 determined ; and the conclusion arrived at is one so stiictly in 

 harmony with the general results obtained by the study of the 

 (apparently) very dififerent phenomena presented by the Genera- 

 tive process of the Cryptogamia, that it justifies the Physiologist 

 in advancing a general doctrine as to the nature of the function, 

 which proves to be no less applicable to the Animal kingdom 

 than it is to the Vegetable. (See Chap. VIII.) 



Among the objects of interest so abundantly offered by the 



