KM BRYOLOGY 



473 



base, and maintains that position^ as the growth proceeds. This is 

 susceptible of no other interpretation than that a suspensor is formed, and 

 that the whole embryogeny is inverted, as compared with that of other 

 Ophioglossaceae where a suspensor is absent. The importance of this 

 lies in its bearing on the general comparison of embryos, and on the 

 estimate of the weight to be attached to some of those differences which 

 have hitherto been made to bear a burden of comparative and phylogenetic 

 argument. If we see that within a narrow circle of affinity the suspensor 

 may be present or absent, and the apex of the embryonic axis be 

 lirected either towards the archegonial neck or away from it, then 

 ich characters become suspect. This will find 

 special application in the comparative study of 

 Lycopodiales and of the Ophioglossales. 

 In the third genus, Helminthostachys, the 

 mngest stages have not yet been seen : but the 

 Id embryo resembles that of Botrychium virgi- 

 inum. 1 It has a large foot derived from the 

 lypobasal region, while the primary root, first leaf, 

 id stem-apex appear to be referable to the 

 >ibasal half. The first 'leaf has a ternate lamina, 

 id reaches the light, but the young plant remains 

 ttached to the prothallus till several leaves have 

 jn formed : one root lies below each of the 

 irliest leaves, but in the older plant this regularity 

 lost (Fig. 267). An endophytic fungus is present 

 the first few roots, though the adult plant is 

 )rmally free from mycorhiza. 

 The character of the prothallus, and perhaps 

 the position of the archegonium upon it, have 

 be taken into account when making comparison 

 of the embryology of the Ophioglossaceae. All their prothalli are 

 typically underground and saprophytic, and the embryos show differing 

 degrees of adjustment to the peculiar conditions thus imposed upon them. 

 In these facts the dominating features of the embryogeny may be found, 

 and they must be borne in- mind not only in any comparison with other 

 Pteridophytes, but also as regards the minor differences which they them- 

 selves show. The most obvious points relate to the development of the 

 earlier leaves : in Botrychium virginianum, Ophioglossum pedunculosum and 

 Moluccanum, and in Helminthostachys the cotyledon itself may be expanded 

 above ground ; but in both of the larger genera there are species which bear 

 the first leaves as rudimentary underground scales : this is seen in O. 

 vulgatum, where the second leaf only is effective for assimilation, and in 

 JB. Lunaria, where a succession of scale-leaves appear, and the eighth 

 leaf is the first that is expanded above ground. The scale-leaves can 



1 Compare Lang, I.e. 



FIG. 267. 



Helminthostachys zeylanica. 

 Young plant attached to pro- 

 thallus. Natural size. (After 

 Lang.) 



