Pleodorina Illinoiensis. 
i 80 
swims freely about, even after the sporangium has grown nearly 
as large as itself. To see the two in that condition, twisting, 
turning, doubling, backing, rolling over one another, reminds one 
of the gambols of two dogs fighting in a half-friendly way in a 
field, or of two equally matched boys wrestling upon a lawn. The 
Chlamydomonas, judging by its antics, is evidently excited and 
uncomfortable under the infliction, but at length it succumbs 
and becomes motionless: its protoplasm disintegrates and dis¬ 
colours, the sporange reaches its full size, the beak develops and 
the zoospores begin to escape through the mucus. When all are 
gone, the mucus has disappeared; the opening, which is often 
wider than a zoospore, is clearly seen, its edges curling back and 
giving the empty sporange an urn-like shape. The complete 
evacuation may occupy a period of more than an hour or two. 
During all the time of observation no resting spores were 
seen, nothing but zoosporangia, and all these were of exactly the 
the same character. Dangeard (“ Le Botaniste,” i., 61, pi. 3, Fig. 
12-15) reported R. globosum as occurring on Chlamydomonas; the 
account given agrees in its details with those of R. acuforme as 
here described, except that the sporangia are said to allow the 
zoospores to escape through four or five little holes, which would 
thus bring the parasite under R. globosum. Nothing approaching 
this was seen in the present instance; in every one of the hundreds 
of cases observed the single opening was always exactly apical. 
NOTE ON PLEODORINA ILLINOIENSIS. 
In June, 1915, I recorded in the New Phytologist (XIV, p. 169) 
the finding of Pleodorina illinoiensis d .iring the preceding spring in 
cart-ruts at Harborne, Warwickshire. The alga occurred, in small 
quantity, in the same unchanged ruts in 1916, and again in larger 
quantity in April, 1917. But this year it was accompanied by about 
equal quantities of Pandorina Morum and Eudorina elegans, as well as 
by other Algae. Moreover, although the elliptical form and the 
posterior protuberances were as marked as ever (or the latter 
even more so), there was intermixed a greater number of trans¬ 
itional stages between it and tbe Eudorina. Therefore the 
suspicion expressed in 1915, that this Pleodorina is merely a well- 
marked mutation of Eudorina —on the way to becoming a species, it 
is true, but not yet completely settled down—is entirely justified. 
This is another instance, added to the many already known but per¬ 
sistently ignored in certain quarters, in which the evolution 
of a species, or even of a genus, is taking place before our eyes. 
W. B. Grove. 
