LVCOPODIACE^. 



405 



differs from that of Ferns and Rhizocarps, taking place perpendicularly to the axis 

 of the archegonium. According to Hofmeister, each of the two cells first formed is 

 divided in Isoetes in a plane at right angles to that of the first division, the relation 

 of which to the first root, the first leaf, the stem, and the foot of the embryo, 

 requires yet further elucidation. The formation of the embryo of Selaginella has 

 recently been investigated in detail by Pfeffer. From an elongation of the upper 

 half of the oospore is formed the Suspensor, a body which is wanting in all other 

 Cryptogams, but universally present in Phanerogams, and through which Sela- 

 ginella consequently approaches flowering plants. The suspensor seldom remains 

 a simple cell; a smaller or larger number of divisions usually takes place in its 

 lower part (Fig. 304, A-D). The embryo itself originates from the lower half 

 of the oospore, which must itself be considered as the primary apical cell of the 

 stem, and the suspensor as its first segment. By the elongation of the suspensor 

 and tlie compression and absorption of the surrounding cells, the mother-cell of 

 the embryo is forced into the endosperm, in which the embryo now undergoes 



Ji 5 



I' M' 



Fig. 304.— Fonnation of the embryo of Stua^infUa .Vayte>isii {After Pfeffer) ; ^/, /? lower part of the suspensor with the 

 first much-ilividci.1 scfjnients of the ciiibrj-o and the apical cell s of the future stem ; M the first leaves ; C apical view of the 

 same ; D the apex seen from above in the act of forming two new apical cells, right and left ; /, //, /// the primary walls 

 of the primary apical cell ; /'— K//' the longitudinal walls by which the two new apical cells are formed. 



further development, as in Phanerogams. In the mother-cell of the embryo two 

 segments are in the meantime cut off by two oblique walls ; out of each pro- 

 ceeds an embryo-leaf (cotyledon), and a longitudinal half of the hypocotyledonary 

 segment of the stem ; the foot and root originating besides from the older 

 segment. Between the two segments in front lies the two-edged apical cell of the 

 stem (Fig. 304, A, B). While the two segments are becoming transformed by a 

 number of cell-divisions into masses of cells, of which an inner mass very soon 

 separates itself as the procambium of the axial bundle and a peripheral mass as 

 dermatogen and periblem, a swelling is produced laterally beneath the first leaf, 

 forming the foot ; by its increase the stem is forced over to the other side (that of 

 the younger segment) ; so that the apex comes to lie horizontally, and afterwards 

 is even directed -upwards (Fig. 303 /) ; and finally the bud, with its first leaves, the 

 cotyledons, grows out 'upright from the apical part of the macrospore when the 

 embryo begins to increase in length. The first root is formed a considerable time 



