EMBRYOGENY OF THE PTERIDOPHYTES 671 
sometimes be equal (Fig. 190 c) they are usually unequal (Fig. 190 D), 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 Sel. spznulosa). 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 Ferns. 
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 Lycopodium cernuum and of Phylloglossum, 
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 /soefes. with 
a similar result (Fig. 191 G). 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, Oph. vulgatum (Fig. 260, 261), Botrychtum Lunaria (Fig. 262, 
263), the cotyledon is small, and probably reduced in accordance with 
the underground habit: in others, Helminthostachys (Fig. 267), Botrychium 
virginianum (Fig. 261) the cotyledon appears above ground as an 
expanded green leaf, and though the apex of the axis is correlatively 
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 Zgucsetum (Fig. 214), though in £. Azemale 
it is apparently higher up (p. 392): but in any case it is clearly lateral 
in Zgutsetum, 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 Oph. moluccanum, Campbell, 1c., p. 189, and Pl. X. 
2Compare p. 469, where Campbell’s alternative view is mentioned. 
