EMBRYOGENY OF THE PTERIDOPHYTES 671 



sometimes be equal (Fig. 190 c) they are usually unequal (Ki^. 190 n), and 

 that the second may be long delayed, and only make its appearance after 

 the shoot issues from the spore : nor is there any constancy in the 

 position of the first relatively to the suspensor and first root (compare 

 Bruchmann, Figs. 62, 63 of ,SV/. sf>itiu/osa}. These examples will serve 

 to show the inconstancy of time and place of origin of the first leaves in 

 the Pteridophytes at large, notwithstanding the constancy seen in Feins. 

 There is, however, one feature that appears constant : it is their orientation 

 relatively to the axis : they all appear to present towards the axis or to 

 that point where the axis will ultimately make its more obvious appearance, 

 a surface that may be recognised as more or less characteristically " adaxial " : 

 even in the extreme cases of Lycopodiutn ccrnnnin and of riiylloglossum, 

 where the number of protophylls is most irregular (Figs. 101, 188, 189), 

 they are not disposed at haphazard, but face towards the point where the 

 apex of the definitive axis appears. This constancy of orientation of the 

 first leaves resembles that of the later leaves, and supports the conclusion 

 already arrived at, that cotyledons and protophylls are essentially of the 

 same category as the later foliage leaves, and are essentially appendages 

 of the axis (pp. 186-7). 



Here it may be well to mention cases of that precocity of the cotyledon 

 which carries with it a correlative delay in development of other parts, but 

 especially of the axis (pp. 183-4). It is seen in Ferns, where the cotyledon 

 is hurried forward to supply a nutritive need, and a correlative delay of 

 the axis is the consequence (Fig. 15). The same is seen in Isoctcs. with 

 a similar result (Fig. 191 o). But perhaps the most remarkable examples 

 are seen in the Ophioglossaceae, plants which show greater adaptive 

 plasticity of the embryo than any others. It has been shown that in 

 certain forms, OpJi. vulgatnm (Fig. 260, 261), Botrycliiion Lunaria (Fig. -<>2, 

 263), the cotyledon is small, and probably reduced in accordance with 

 the underground habit: in others, Helminthostachys (Fig. J(>7), Hotrychium 

 virginianum (Fig. 261) the cotyledon appears above ground as an 

 expanded green leaf, and though the apex of the axis is correlative!} 

 delayed, it is still recognisable. But in others again the cotyledon is 

 precociously developed to such a degree that it is difficult or impossible 

 to recognise the apex of the axis ; * this may be held to be an extreme 

 case bearing with it correlative consequences which have completely upset 

 the balance of parts in the embryo.- 



The time and place of origin of the first and subsequent roots is open 

 to variation. In Ferns it arises in the hypobasal hemisphere, and this is 

 the case also in certain types of Et/iiisc/i/i/i (Fig. 214), though in K. liicmalc 

 it is apparently higher up (p. 392): but in any case it is clearly lateral 

 in E</i(ise/itm, and the condition in Ferns appears to be only a less bulky 

 variant on the same type. The apparent difference in exact point of 



1 Of/i. iiio/iiccanniii, Campbell, /.<., p. 189, and I'l. X. 



- Compare p. 469, where Campbell's alternative vk-\\ is mentioned. 



