EMBRYOLOGY 



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 

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

 such characters become suspect. This will find 

 its special application in the comparative study of 

 the Lycopodiales and of the Ophioglossales. 



In the third genus, Helniintlwstachys, the 

 youngest stages have not yet been seen : but the 

 old embryo resembles that of Botrychium virgi- 

 nianuml It has a large foot derived from the 

 hypobasal region, while the primary root, first leaf, 

 and stem-apex appear to be referable to the 

 epibasal half. The first leaf has a ternate lamina, 

 and reaches the light, but the young plant remains 

 attached to the prothallus till several leaves have 

 been formed : one root lies below each of the 

 earliest leaves, but in the older plant this regularity 

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

 in the first few roots, though the adult plant is 

 normally free from mycorhiza. 



,, , .- , i ,, j i H elminthostachys zcvlanii.,1. 



The character of the prothallus, and perhaps y ou n- plant attached to pr >.- 



.1 , r ,1 i . i lhallus. Natural >ize. (. \fu-r 



also the position of the arcnegomum upon it, have Lang.) 

 to 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 

 Motitccanum, 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 

 B. 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 Lrmg, l.<\ 



FIG. 267. 



