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,Gamophyta 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 Coleochaete 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 (87), 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. Oedogoniwm 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 geries, 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 (88) serve to indicate how slight is the actual difference 
~~), Bonavla: Phil. Notes on Botan. Subj. (1892). 
(38), Belajeff: ZurLehre von dem Pollenschlauche derGymnospermen. Bericht. Deutsch 
Botan. Gesellsch. IX. 274-286 (1891). 
