THE HIGHER CltYPTOGAMIA. 371 



mode of appearance, and the abundance, of both kinds of 

 reproductive cells, are favorable to the observation of the 

 origin of spermatozoa in the smaller archegonial prothallia, 

 and not less so to the observation of the separate develop- 

 ment of the microspores and macrospores. 



The germination of Isoetes, like that of the Ophioglosseee, 

 is distinguished from that of the vascular cryptogams which 

 have green prothallia in one essential point. In these the 

 lateral cell of the limited primary axis of the embryo, from 

 whose multiplication the (secondary) principal axis pro- 

 ceeds, lies in the apical region of the former. The leaf- 

 bearing principal axis developes the first leaf on the side 

 which is turned away from the apex of the primary axis and 

 towards the exit of the archegonium. The first leaf lies 

 above the principal bud, between it and the mouth of the 

 archegonium, as is the case with the Ferns and the Rhizo- 

 carpese. In Isoetes, on the other hand, the bud of un- 

 limited growth lies near the first adventitious root, close 

 under the canal of the archegonium, and the first leaf lies 

 under that bud. Judging from the position of the first 

 root on the germ-plant, Selaginella would exhibit a similar 

 state of affairs, were it not for the fact, that here the secondary 

 principal axis of the plant, instead of producing a leaf 

 close above its point of origin, divides into two branches, 

 having previously grown considerably in length, and having 

 produced a pair of opposite leaves. 



In its vegetative development as well as in its fructifica- 

 tion and germination, Isoetes exhibits a remarkable agree- 

 ment with the Lycopods, in the fact that the wood-forming 

 tissue has no parenchymatous pith in the centre, but 

 occupies the whole of the longitudinal axis in the form of 

 a homogeneous woody body. Nageli's investigations* have 

 shown that in Lycopodiimi a circle of vascular bundles is 

 visible at first, but that after the differentiation of the 

 circularly-arranged longitudinal strings of a delicate cam- 

 bium, the whole of the axile tissue of the stem enclosed by 

 the latter enters into the formation of the wood, and is 

 afterwards changed from parenchymatal into prosenchy- 

 matal cells of various kinds. Thus in nearly allied plants, 



* ' Zeitschrift fur Botanik,' H. 3 and 1, p. 140. 



