SEXUAL REPRODUCTION OF THALLOPHYTES. 297 
Schwendener’s view has been discussed. ‘The general result 
has certainly been to confirm it. Lichens must, therefore, be 
degraded from their position as a principal division of 
Thallophytes and be referred to ascomycetous Fungi as a 
characteristic group of parasitic forms. 
In 1872 Cohn! went a step further in abolishing the 
division of Thallophytes into Alge and Fungi—the two 
groups which survive after the reduction of Lichens, But, as 
Sachs points out, the characters which Cohn employs in esta- 
blishing new groups are of quite unequal value, being some- 
times morphological, sometimes physiological. There can be 
no real comparison of such groups as Zygosporee, Tetra- 
sporee, and Zoosporee. 
The classification which Sachs himself has proposed is 
not open to this objection, being based upon the progressive 
differentiation of the reproductive organs. It is obviously, 
therefore, a classification which, on the one hand, has only 
been rendered possible by modern investigation, and, on the 
other, is subject to continual correction. He has followed 
Cohn in attaching little value to the separation of Alge from 
Fungi. Ue points out that each of these assemblages of 
organisms may be arranged as a morphological series which 
runs parallel with the other. The essential distinction 
between them reduces itself to a difference, which, amongst 
higher plants, is regarded as an adaptive one. Alge 
are Thallophytes in which chlorophyll is present; Fungi 
are Thallophytes in which it is absent. Cohn and Sachs 
have attached no more importance to this than is done 
in the case of Phanerogams. The saprophytes Coral- 
lorhiza innata and Epipogium Gmelini hold their proper 
systematic position amongst Orchidacee quite irrespectively 
of the fact that they are as destitute of chlorophyll as an 
Agaricus. 'The parasitic Phanerogams are also distributed 
amongst the forms with which they possess morphological 
relationship, and are not placed apart in any special group 
solely on account of their physiological peculiarities. 
III. 
The fundamental difference between plants and animals 
resolves itself into a difference of nutrition. Animals are 
capable, plants are incapable of the ingestion of solid food. 
A process of digestion, by which nutritious material may be 
reduced from the solid to the liquid form, is therefore neces- 
sary to animals, unnecessary to plants. ‘The morphological 
' Hedwigia, 1872, p. 18; ‘Journ. of Bot.,’ 1872, p. 114. 
