18 Veir Brecuer Wirrrock. 
The prolific cells are thus made to differ from the common vegetative 
cells by containing a greater abundance of chlorophyll, and particularly 
a more plentiful supply of starch. The cells which are transformed 
into prolific cells generally belong to the principal filament of the thallus, 
and are always inclosed — not terminal — cells. Besides in sterile 
specimens, prolific cells are also found in the sterile part of half-fertile- 
half-sterile individuals. In P. Cleveana nob. I have, even in purely 
fertile specimens, found cells which can hardly be anything but prolific 
cells; see for instance pl. 4, fig. 18 p and pl. 5, fig. 2 p. That these 
cells are not spores is easily seen from the fact that a passing of chloro- 
phyll to them cannot have taken place from’ any quarter; but that they 
serve a reproductive purpose is rather clearly indicated by their rich 
contents. The irregularly fusiform cells represented pl. 1, fig. 15 and 
marked p, p’, which belong to a fertile specimen of P. polymorpha nob., 
may also perhaps be prolific cells. If it be so, it is the more remark- 
able, because the upper one, p, has already formed a small spore, ste, in 
its top, and the lower, p’, is evidently on the point of doing so. It 
would then come to pass, that sister cells of spores, so-called subsporal 
cells, which are otherwise always destined for destruction, would them- 
selves serve as reproductive cells. The possibility of this would of 
course be~-evidenced by the subsporal cells being, in this case, so rich 
in chlorophyll, as a consequence of their delivering but an inconsider- 
able part of their contents to the comparatively small spores. 
From the exposition given above we find, that the prolific cells 
arise immediately out of the common vegetative cells, by these cells 
being filled with richer store af reserved food; but without any previous 
enlargement or change as to the outer shape.*) In a species of Clado- 
phora, the common C. fracta Dillw., growing in fresh water, we know 
already from the results of the observations of Kiitzing, exhibited m 
Phycol. Gener. page 263 and 264 (with beautiful illustrations on pl. 11), 
that such a formation of prolific cells takes place; but the prolific cells 
here differ from the common vegetative cells not only by the nature of 
their contents, but also by their shape, which is not cylindrical, but 
irregularly rounded or almost pear-shaped. 
The following paragraph will give an account of the germination 
of the prolific cells as well as of that of the spores. 
1) Only in the subsporal cells of P. polymorpha nob. mentioned just above 
(represented pl. 1, fig. 15 p, p’), — supposing these to be really prolific cells, — an 
enlargement and change of shape have taken place. 
