188 M. Muller on the Germination of Isoetes lacustris. 



This is very apparent when the second leaflet has become con- 

 siderably elongated beyond the margin of the vagina (figs. 22 d, 

 23 d), and it is most closely connected with the furrow of the 

 first leaf. Looked at from this point, the vagina appears abruptly 

 cut off. 



By the time the third leaflet appears, the vagina has vanished 

 and the bases of the two first leaves surround the third as a 

 sheath, as is the case in the full-grown plant (fig. 24 d ) . 



6. The Second Leaf. — The rudiment of this also is formed at 

 a very early epoch, and in fact at the time when the first leaf is 

 still a mother-cell. Consequently two mother-cells, for two dif- 

 ferent organs, occur close together in the vagina, which itself is 

 in the earliest stage of formation (figs. 12 c, 13 b, 15 e, 16 d). 



While the mother-cell of the scale grows into a disc-shaped 

 body, the mother-cell of the second leaf expands more and more 

 in a globular form. It is soon observed that, already in this 

 form, cellular tissue has been produced in its interior (fig. 18). 

 This epoch is contemporaneous with the perfect formation of the 

 scale of the first leaf. From this cause the vagina has become 

 drawn so closely round the second leaflet (figs. lSi,20h), that 

 the latter is ensheathed in it, as an obtuse conical body. 



Very soon, however, the first leaflet rises out far beyond the 

 vagina, at the same period when this has acquired a rather deli- 

 cate membrane (fig. 21 d, and the vagina^). The leaflet is by 

 this time green, and when seen from the side, as in fig. 21 d, it 

 appears somewhat compressed on two sides. No great changes go 

 on meanwhile in the second leaflet until it emerges from the now 

 much-slongated vagina (fig. 22 e). By that time the second scale 

 has been formed at the base, inside the vagina. The most 

 important change however has happened at the base, underneath 

 the vagina. Here a gradually-formed protuberance displays itself, 

 composed of very delicate cellular tissue (fig. 22/). This is the 

 rudiment of the second rootlet, or that of the second leaf. Its 

 further development resembles that of the first rootlet. As it be- 

 comes elongated the vessels may soon be observed, of which two 

 again display themselves here (fig. 23 e). The cells are at first 

 delicate and full of cytoblastema. Subsequently, when consi- 

 derable elongation has taken place, they become emptied and of 

 longer shape, exactly as in the first rootlet, wholly as in the 

 leaflet itself. 



I have already mentioned that about this time the vascular 

 bundle of the first rootlet has become divided into two (figs. 22, 

 23). 



[To be continued.] 



