356 LYCOPODIALES 



(B) LIGULATE LYCOPODIALES. 



It is an unfortunate circumstance that the embryogeny of fossils is 

 usually inaccessible, for that of the dendroid Lycopods would greatly 

 strengthen views as to their relation to modern forms. As it is, Sela- 

 ginella and Isoefes provide the only facts of the embryogeny in the 

 Ligulate Lycopods : it will be seen that they are strangely divergent in 

 the form of the embryo. 



It has been pointed out that Selaginella spinulosa may be held to 

 be more primitive as regards the morphology of the mature plant than 

 the dorsiventral species of the genus \ and further, it has been seen that 

 it differs from them anatomically, showing a vascular structure which is 

 probably more primitive also. This gives a special interest to its em- 

 bryology, which has been fully worked out by Bruchmann. 1 The early 

 stages are essentially as in Lycopodium, resulting in a suspensor, and two 

 tiers of four cells each, forming the embryo : the whole structure is at 

 first straight, with the apex flattened (Fig. 190 A, B). The susp'ensor 

 remains as in Lycopodium, and is a means of thrusting the embryo down- 

 wards into the tissue of the prothallus. The lower tier of cells of the 

 embryo (i.e. that between walls i., i. and iv., iv. in Fig. 190 A and c) itself 

 forms the hypocotyl, which may here be greatly elongated and curved. 

 and becomes thus a prominent feature of the embryo ; at its base, in 

 close relation to the suspensor, the first root arises in a lateral position. 

 The products of the upper tier at first remain small (i.e. above wall 

 iv., iv., Fig. 190 A, c) : the formation of the first cotyledon may in some 

 cases be long delayed, sometimes it may still be wanting even when the 

 axis has already curved obliquely to the suspensor. The second cotyledon 

 may be even longer delayed : in some cases it only appears after the shoot 

 issues from the spore. But sooner or later two opposite but unequal 

 cotyledons successively make their appearance. Their orientation relatively 

 to the suspensor is liable to vary. The apex of the axis, 'which has no 

 single initial cell, lies between them, originating from the centre of the 

 flattened apex of the embryo (Fig. 190 A, c, D). As the hypocotyl 

 elongates the embryo curves so that the axis takes a vertical position, while 

 the suspensor is pushed to one side by the growing root. Finally the 

 shoot emerges above ground, and the two cotyledons, developing at last 

 to equal size, appear as green assimilating leaves (Fig. 190 G, H). 

 According to Bruchmann, no enlarged " foot " is formed in this species, 

 and the same appears to be the case in Selagintlla apus. 



Comparing this embryogeny with that so well known in S. Martensii, 

 there is essential similarity in the disposition of the parts. The chief 

 difference lies in the presence of an haustorial swelling of the hypocotyl 

 in S. Martensii, which has been called a "foot," and in the fact that 

 single initials are found at the apices of stem and root : this accords 



^ U liters, ueber ''''Selaginella spinulosa," Gotha, 1897. 



