18 .Veit Brecher Wittrock. 



Tlie 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 pi. 4, fig. 18 p and pi. 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 pi. 1, fig. 15 and 

 marked p,})'-, which belong to a fertile specimen of P. poh/inorpha noh., 

 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, .s^c, in 

 its top, and the lower, j/, 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, b}^ 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 in 

 Phycol. Gener. page 263 and 264 (with beautiful illustrations on pi. 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 cyhndrical, 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. 



') Only in the subsporal cells of P. pohjiiiorplia nob. mentioned just above 

 (represented pi. 1, fig. 15 p, ]}), — supposing these to be really prolific colls, — an 

 enlargement and change of shape have taken place. 



