234 Campbell . — Contributions to the 
of the exospore renders it quite impossible to judge of the 
stage of development in the living spore, we can only judge 
of the time necessary for the different stages of growth, by 
a comparison of sections, and this, of course, can give only an 
approximate idea. Of the first lot, sown Sept. 27, the 
youngest spore, in which the first division of the primary 
nucleus was observed, was nineteen days old ; but in one case, 
at least, a spore of the same age had advanced beyond this 
point, and to judge by comparison with others, was probably 
two or three days in advance of those in which the first divi- 
sion of the primary nucleus was seen. The youngest full- 
grown prothallia observed were from a week to ten days older, 
and the first young plants broke through the prothallium 
almost exactly one month from the time the spores were 
placed in water. The germination of the microspores is more 
rapid, but the exact time was not noted. Owing to the 
transparency of the exospore the time required can be de- 
termined with much greater exactness than is the case with 
the macrospores. Spores sown later germinate more rapidly. 
Sowings were made Dec. 13, and just three weeks later 
(Jan. 2) the first young plants were noted, the leaf being 
already green and about one centimetre in length. Micro- 
spores sown about the same time produced the first ripe 
spermatozoids in two weeks. 
The Male Prothallium. 
The microspores are borne in the sporangia at the bases of 
the inner leaves, and are of the bilateral type of spores, i. e. 
each is in form the quadrant of a sphere. The exospore is 
nearly colourless in the species under consideration, smooth, 
and sufficiently transparent to allow a plain view of the in- 
terior of the spore. Owing to this the development of the 
antheridium is easily followed in the living spores. As the 
germination of the microspores of I. lacustris has already 
been exhaustively treated by Millardet 1 and Belajeff 2 , and 
I. echinospora does not differ in any respect from that species, 
Loc. cit. 
2 Loc. cit. 
