EMBRYOLOGY 471 
both for storage and as a haustorium (Fig. 263 a). Even at this early 
stage the embryo may contain an endophytic fungus. The formation of 
a succession of roots may then follow, while the growth of the bud 
remains almost quiescent, though it forms a succession of small leaves 
(Fig. 263 B): of these about the eighth appears above ground, the rest 
serving only for protection to the bud. It is interesting, however, to note 
that a rudimentary fertile 
spike may be found even 
on some of these rudimentary 
scale-leaves. From this point 
onwards the development is 
as in the mature plant. Com- 
paring this development with 
that in B. wirginianum, the 
relative position of the several 
parts is essentially the same: 
the chief differences are in 
their proportion. The root 
and foot are larger, and the 
axis later in definition: also 
there is the fact that the first 
few leaves are scale-leaves, 
whereas in B. wirgrnianum 
the first leaf is itself ex- 
panded above ground. The 
same difficulty holds here as 
before in defining whether the 
root is hypobasal or epibasal 
in origin. It is from such 
differences as these existing Fic. 264. 
within a narrow circle of Boleweliune (Stapirtiin is abliquain, Nails Phote micro: 
affinity that a. true estimate Hye Toots already prattaded Nam the under side of the vane 
Of the value of embryonic qgRby'e, «qarchegominm: soampemors eoatemdp; Sit 
characters may be derived. 
But these differences are of small account compared with the divergence 
from the general type of the genus shown by another species, B. obliguum, 
Muhl. H.L. Lyon has described how its zygote does not develop directly 
into the embryo as in other species, but first gives rise to a suspensor, 
which burrows into the tissue of the gametophyte in the manner characteristic 
of certain Lycopods. -The embryo itself is formed at the tip of this 
suspensor, and its parts are differentiated relatively early (Fig. 264). The 
parts themselves are essentially similar to those of other species of the 
genus: the first leaf (cotyledon) appears on the side of the axis directed 
upwards, and it breaks through the upper surface of the prothallus: the 
root originates on the side directed downwards, and it emerges on its 
