658 Blackman .— The Primitive Algae 
hollow of the chloroplast contains granular protoplasm in 
which the nucleus is situated. Finally, somewhere on the 
periphery of the anterior half of the protoplast is a bright red 
pigmented disk, the eye-spot or stigma, which is in some way 
associated with the directional reaction of the organism to 
radiation. 
Most genera of unicellular Algae of simple form (in opposi¬ 
tion to Desmids and Diatoms) consist of only a very few, 
difficultly characterized species. Quite the reverse holds with 
Chlamydomonas , but in distinguishing the species, the shapes 
and sizes of the individuals are of no significance, and the 
cell-walls show practically no variation : cytological characters 
are alone available. Yet it appears that at least eighteen 
good species may be precisely diagnosed in this way. 
Wille, in 1890, allowed some six species. Goroschankin 
(’ 91 ) in the next year published an admirable study of the 
specific characters in this genus, and defined clearly nine 
species. These were all carefully figured, and the life-history 
was followed in every case. The characters are so precise 
that the author is able to draw up a tabular analytical key, 
by which the different species may be distinguished in their 
motile vegetative condition. The sort of differences on which 
this is based may be briefly enumerated. The chloroplast 
may be solid or reticulate, ring or basin shaped ; the contrac¬ 
tile vacuoles, two or three in number; the cilia, two or four, 
short or long ; the pyrenoids, absent or single or two, boat¬ 
shaped or spherical; the eye-spot shaped like a rod or a disk ; 
and, finally, the zygote may be smooth-walled or spiny. 
Higher up in the green Algae uniform cytological characters 
characterize genera and families, but in this primitive type 
we learn that they only hold for the species. 
Franck, in 1892, in a revision of the genus, maintained that 
these cytological differences were not really constant, and 
proposed to reduce largely the number of good species. No 
experimental evidence of the passage of one form into another 
was, however, presented. 
Schmidle, in 1893, described a very interesting new species. 
