TRANSACTIONS OF SECTION K. 923 



1 will conclude my remarks on morphology witli a few illustrations of the aid 

 which the advance in this department has given to the progress of classiflcation. 

 For instance, Linnajus divided plants into Phanerogams and Cryptogams, on the 

 ground that in the former the reproductive organs and processes are conspicuous, 

 whereas in the latter they are obscure. In view of our increased knowledge of 

 Cryptogams this ground of distinction is no longer tenable ; whilst still recog- 

 nising the validity of the division, our reasons for doing so are altogether diflerent. 

 For us. Phanerogams are plants which produce a seed ; Cryptogams are plants 

 which do not produce a seed. Again, we distinguish the Pteridophyta and the 

 Bryophyta from the Thallophyta, not on account of their more complex structure, 

 but mainly on the ground that the alternation of generations is resular in the two 

 former groups, whilst it is irregular or altogether wanting in the latter. Similarly 

 the essential distinction between the Pteridophyta and the Bryophyta is that in 

 the former the sporophyte, in the latter the ga'metophyte, is the p'repouderating 

 form. It has enabled us further to correct in many respects the classifications of 

 our predecessors by altering the systematic position of various genera, and some- 

 times of larger groups. Thus the Cycadaceaj have been removed from among the 

 Monocotyledons, and the Conifers from among the Dicotyledons, where 

 de Candolle placed them, and have been united with the Gnetaceie into the 

 sub-class Gymnospermffi. The investigation of the development of the flower, in 

 which Payer led the way, and the elaboration of the floral diagram which we owe 

 to Eichler, have don(3 much, though by no means all, to determine the ailinities of 

 doubtful Angiosperms, especially among those previously relegated to the lumber- 

 room of the Apetalffi. 



Anatomy and Histology. 



Passing now to the consideration of the progress of knowledge concerning the 

 structure of plants, the most important result to'be chronicled is the discovery that 

 the plant-body consists of living substance indistinguishable from that of which 

 the body of animals is composed. The earlier anatomists, whilst recognising the 

 cellular structure of plants, had confined their attention to the examination of the 

 cell-walls, and described the contents as a watery or mucilaginous sap, without 

 determining where or what was the seat of life. In 1831 Robert Brown dis- 

 covered the nucleus of the cell, but there is no evidence that he regarded it as 

 living. It was not until the renascence of research in the forties, to which I have 

 already alluded, that any real progress in this direction was made. The cell- 

 contents were especially studied by Naegeli and by Mohl, both of whom recognised 

 the existence of a viscous substance lining the wall of all living cells as a ' mucous 

 layer ' or ' primordial utricle,' but diflering chemically from the substance of the 

 wall by being nitrogenous: this they regarded as the living part of the cell, and 

 to it Mohl (1846) gave the name 'protoplasm,' which it still bears. The full 

 significance of this discovery became apparent iu a somewhat roundabout way. 

 Dujardin, in 1835, had described a number of lowly organisms, which he termed 

 Infusoria, as consisting of a living substance, which he called ' sarcode.' Fifteen 

 j-ears later, in a remarkable paper on Protococnts phaialis, Cohn drew attention to 

 the similarity in properties between the ' sarcode ' of the Infusoria and the living 

 substance of this plant, and arrived at the brilliant generalisation that the ' proto- 

 plasm ' of the botanists and the 'sarcode' of the zoologists are identical. Thus 

 arose the great conception of the essential unity of life in all living things, which, 

 thanks to the subsequent labours of such me'n as de Bary, Briicke, '^and Max 

 Schultze, in the first instance, has become a fundamental canon of Biology. 



A conspicuous monument of this period of activity is the cell-theory pro- 

 pounded by Schwann in 1839. Briefly stated, Schwann's theory was that all living 

 bodies are built up of structural units which are the cells : each cell possesses an 

 independent vitality, so that nutrition and growth are referable, not to the 

 organism as a whole, but to the individual cells. This conception of the structure 

 of plants was accepted for many years, but it has had to give way before the 

 advance of anatomical knowledge. The recognition of cell-division as the process 



