SEPTEaiBEE 28, 1900.] 



SCIENCE. 



467 



been threshed out at recent meetings of 

 this Section. The second problem is as to 

 the origin of the sporophylls, and, indeed, 

 of all the various kinds of leaves of the 

 sporophyte in the higher plants. It is sug- 

 gested, on the one hand, that the sporophylls 

 of the Pteridophyta have arisen by gradual 

 sterilization and segmentation from an un- 

 segmented and almost wholly reproductive 

 body, represented in our day by the sporo- 

 gonium of the Bryophyta ; and that the 

 vegetative leaves have been derived by 

 further sterilization from the sporophylls. 

 On the other hand, it is urged that the 

 vegetative leaves are the more primitive, 

 and that the sporophylls have been de- 

 rived from them. It will be at once ob- 

 served that this second problem is in- 

 timately connected with the first. The 

 sterilization theory of the origin of leaves 

 is a necessary consequence of the antithetic 

 view of the alternation of generations ; 

 whilst the derivation of sporophylls from 

 foliage- leaves is similarly associated with 

 the homologous view. Here, again, ex- 

 ercising a wise discretion, I will only ven- 

 ture to express my appreciation of the im- 

 portant work which has been done in 

 connection with this controversy — work 

 that will be equally valuable, whatever the 

 Issue may eventually be. 



I will conclude my remarks on morphol- 

 ogy with a few illustrations of the aid 

 which the advance in this department has 

 given to the progress of classification. For 

 instance, Linnaeus divided plants into Phan- 

 erogams 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 ten- 

 able ; whilst still recognizing the validity of 

 the division, our reasons for doing so are 

 altogether different. For us. Phanerogams 

 are plants which produce a seed ; Crypto- 



gams are plants which do not produce a 

 seed. Again, we distinguish the Pterido- 

 phyta a,nd the Bryophyta from the Thallo- 

 phyta, not on account of their more com- 

 plex structure, but mainly on the ground 

 that the alternation of generations is regular 

 in the two former groups, whilst it is ir- 

 regular 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 gametophyte, is the preponderating 

 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 sometimes 

 of larger groups. Thus the Cycadacese 

 have been removed from among the Mono- 

 cotyledons, and the Coniferse from among 

 the Dicotyledons, where de Candolle placed 

 them, and have been united with the Gneta- 

 cecB into the sub-class Gymnospermse. 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 done much, though 

 by no means all, to determine the affinities 

 of doubtful Angiosperms, especially among 

 those previously relegated to the lumber- 

 room of the Apetalse. 



ANATOMY AND HISTOLOGY. 



Passing now to the consideration of the 

 progress of knowledge concerning the struc- 

 ture of plants, the most important result to 

 be chronicled is the discovery that the 

 plant-body consists of living substance in- 

 distinguishable from that of which the 

 body of animals is composed. The earlier 

 anatomists, whilst recognizing the cellular 

 structure of plants, had confined their at- 

 tention 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 discovered the nucleus of 



