M. Miiller on the Germination of Isoetes lacustris. 327 



tary body, inside the ovule, but outside this, beside the terminal 

 bud (fig. 25 b) : therefore the ovule is never perforated by a root 

 as in Isoetes. 



The most important distinction between the genera, is that in 

 Selaginella an actual terminal bud is produced, in Isoetes none, 

 which is naturally explained by the fact, that in Selaginella, elon- 

 gated axes are developed, while in Isoetes the axis always remains 

 short and appears as a rhizome. On this account also the indi- 

 vidual organs are never produced symmetrically here in Isoetes, 

 as they are so strictly in the terminal bud of Selaginella. 



These may be taken as the most essential points which allow 

 of comparison in the young embryos of the two genera. We 

 trace in them all the similarity which may be concluded from the 

 relationship, but also all the dissimilarity that has its ground in 

 the different type of the two genera, which is at once expressed 

 in the course of development. The most essential relationship 

 between the two, however, is above all the formation of the 

 embryo in the interior of an ovule, without a pollen-tube. 



It is exceedingly desirable that, in order to complete our 

 knowledge of the mutual relationship, some one may be able 

 very shortly to furnish the history also of the earliest stages of 

 development of the Selaginella. 



Possible Results. 



After it has been shown in the foregoing how a cell is able to 

 form in an independent manner, inside a perfectly closed organ, 

 without a pollen-tube ! I might repress all further conclusions 

 against those who derive the formation of the embryo of sexual 

 plants from a constricted pollen-tube. But I have one more 

 observation on Isoetes to subjoin, which I could not pass over in 

 silence, since it appeared to me to possess great importance in 

 regard to that controversy. 



It is well known that in many plants two embryos sometimes 

 appear within one and the same ovule. This phenomenon is 

 explained by Schleiden by the penetration of two pollen-tubes. 

 I have observed the same phenomenon in Isoetes, where two in- 

 dependent embryos had been formed in one and the same ovule, 

 and I have represented the case in fig. 19. It was evident how- 

 ever that neither of the embryos were in a good condition; 

 though they were normally formed, both suffered from it, in va- 

 rious places. One was developed considerably at the cost of the 

 other, and possessed two vascular cords in its root. Nothing of 

 these could be seen in the other. It would have fared badly with 

 both also, afterwards, since neither of them had any of the starch, 

 the so necessary nutriment, in the alimentary organ (fig. 19 e). 



