93 
The Classification of the Algae. 
new system of these forms has become a kind of sport to the Algo- 
logist, and while probably the great majority of existing generic 
forms have now been described, we are in need of a Good deal more 
detailed information as to their minute structure and life-history 
before we shall reach any sort of finality in their classification. 
They are certainly a most difficult group to deal with, since the 
genera are so numerous, their external form so various, and their 
cell-structure often difficult to observe with sufficient accuracy, 
unless good cytological methods, difficult to apply in many cases, 
are employed. Professor Oltmanns, it is interesting to note, 
separates Volvocales (the motile) from Protococcales (the motion¬ 
less forms) and includes Tetrasporaceae (in a somewhat narrow 
sense) in the former. While there can be no doubt that some of the 
mucilaginous immotiie types are extremely closely related to the 
Chlamydomonadines, it seems unnatural to separate them altogether 
from numerous other unicellular immotiie forms which our author 
puts in Protococcales. Surely it is most natural to draw the line 
at the point where the immotiie phase of the life-history becomes 
dominant. Professor Oltmanns artificially simplifies his problem to 
some extent by omitting all reference to a certain number of genera. 
The “ Scenedesmacea; ” practically correspond with the Selenas- 
traceae plus the Phytheliaceas of the “ Revision,” and are no doubt 
a natural group. Of the remaining families there is not very much 
that need be said. 
A group Ulotrichales is adopted by Professor Oltmanns to 
include the branched and unbranched filamentous types (the 
Ulotrichales of the “ Revision ” together with the Ulvaceae and the 
QEdogoniaceae). Neither the parenchymatous structure of the 
former, nor the characteristic motile cells and other peculiarities of 
the latter, seem to Professor Oltmanns to constitute sufficient 
reason for placing them in separate groups. 
The genera included in the Chietophoraceae, whose limits differ 
widely from those given by Wille, mainly follow the arrangement 
adopted in the “ Revision,” in which, largely on the ground of 
Huber’s excellent researches, the epiphytic and endophytic forms 
were regarded as progressive reduction-series from the primitive 
Stigeoclonium- type. In the present work however AphauocJuete is 
given a separate family on the ground of its sexual reproduction. 
It is interesting to note also that he is inclined to accept Chodat’s 
report of the existence of aplanospores, zoospores and gametes in 
PIcurococcus and to follow this author in considering the genus a 
reduced Chaetophoraceous type. Certainly the cell-division and 
