INTRODUCTION. 25 



contractile vesicles and chlorophyll, may perhaps be safely set 

 down as a plant. Chondrioderma difforme, with its plasmodial 

 growth, its adelphotropic swarmspores, contractile vesicles and 

 chlorophylless nutrition, may be as safely set down as an 

 animal. This point admits, however, of extended argument, 

 which would here be out of place, and the impression must not 

 be received that it is proposed to give it an off-hand settlement. 

 With reference to the Thallophyta of Engler it is apparent 

 that this group is a catch-all. Forms widely distinct in 

 phylogeny, physiology and structure are indiscriminately 

 lumped together. Plants which have been limited above as 

 Protophyta, Gamophy ta and Thallophyta (in the narrower sense) 

 are here tumbled into one broad and vague category. It is 

 true that a single clue will perhaps never lead one out of the 

 labyrinth, but in the face of the charge, that embryologists are 

 rashly endeavoring to base their classifications upon single 

 and possibly uncertain groups of facts, it is urged that the 

 Thallophyta of Engler has neither coherency nor limitability. 

 It serves to delimit the algae in a manner which throws into 

 low relief the probable relationship between the algae and the 

 higher plants. From ColeocJiaete to Riccia is not a long step, 

 and it should not be made to appear that a taxonomic chasm 

 separates these forms. Apart from insanities of homologising, 

 such as those of Bonavia (37), there are actual contact points 

 between the "'sea-weeds" and the lower Hepaticae and a natural 

 classification should recognise these contact-points. The 

 Embryophyta of Engler ( and to Engler alone may be ascribed 

 this classification) are very nearly co-extensive with the 

 Sporophyta as limited above. Oedogoniurn. and allied forms are, 

 however, omitted and, in our belief, this does violence to the 

 natural arrangement. Provision should be made for the union 

 of these related plants, for in the belief of the writer, next to 

 sexuality, the development of sporophytes is the most funda- 

 mental fact of plant- comparative- physiology. Again the divis- 

 ion of the Sporophyta need not be made upon those struc- 

 tural gametophytic characters employed by Engler when he 

 divides his Embryophyta into two series, based upon the devel- 

 opment of ciliated spermatozoids in the lower and the produc- 

 tion of pollen-tubes in the upper. The researches of Belajeff 

 alone (38) serve to indicate how slight is the actual difference 



(37), Bonavia: Phil. Notes on Botan. Subj. (1892). 



(38). Belajetf: ZurLehre von (lemPollenschlauchederGymnosperinen. Baricht. Deutsch 

 Botan. Gesellscb. IX. 274-286 (1891). 



