i 35 
Cytology and Classification. 
which according to West’ “ seems a very natural one,” is divided 
from the Chlorophyceae by the possession of parietal discoidal 
chromatophores of yellowish green colour without pyrenoids, and a 
fatty reserve substance in lieu of starch. 
The main character separating the Fungi from the Algae 
is a cytological one,—the absence of chlorophyll. Also the cell- 
walls shew some difference, those of the Algae consisting of cellulose, 
while in many Fungi 2 this is replaced by chitin. The Mosses 2 and 
Liverworts 3 only give cellulose reactions after prolonged treatment 
with potash, owing to the combination of the cellulose with aromatic 
antiseptic bodies such as sphagnol. Amongst the Ferns and 
Phanerogams there seems to be nothing sufficiently constant in the 
structure or composition of the cell walls to be of use in classi¬ 
fication. 
Chloroplasts are not the only cell contents which have some 
systematic value. Pyrenoids, for instance, are never found outside 
the Algae except in Anthoceros. The form of starch grains seems 
to be a character that might be more made use of than it is ; 
the Chenopodiaceae have compound grains, while in Rye, Wheat, 
and Barley they are simple and lenticular, and so on. 
The question of how far the chief organ of the cell, the nucleus, 
gives serviceable indications of affinities is at present very difficult 
to answer, since our knowledge of nuclear structure in the different 
groups is so very incomplete. We can trace a certain general 
advance in complexity as we pass from lower to higher forms, and 
though whenever a nucleus occurs with a simple structure and a 
simple method of division we are confronted with the question of 
whether it is primitive or reduced. The Myxophyceae (or Cyano- 
phyceae), which are probably the most lowly of the Algae, used to be 
regarded as possessing no specialised nucleus at all. There is 
however a central body of a curious radiating form without, it is 
true, either nuclear membrane or nucleolus, which seems to possess 
some of the attributes of a nucleus. In the other Algae we 
meet with a more normal type of nucleus, and some cases of 
karyokinesis have been described. Unfortunately too little work has 
been done on the nuclear structure of the Algae in general to 
allow us to draw any conclusions as to its value in determining 
their affinities ; the same holds good for the Fungi. Amongst the 
1 G. S. West. “ The British Freshwater Algze.” Cambridge, 1904. 
1 C. van. Wisselingh, “ Mikrochemische Untersuchung iiber die 
Zelhviinde der Fungi.” Reviewed Bot. Zeit. September 1, 
1898. 
3 F. Czapek. “ Zur Chemie der Zellmembranen bei den Laub- 
und Lebermoosen.” Reviewed Bot. Zeit. December 16, 1899. 
