EMBRYOLOGY 





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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. virginianum, 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 

 tew leaves are scale-leaves, 

 whereas in B. virginianuin 

 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 

 within a narrow circle of 

 affinity that a true estimate 

 of the value of embryonic 

 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. obliquum, 

 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 



FIG. 264. 



Botr\ ( /limit (Sceplridivm) ob.iqiann, Muhl. Photo micro- 

 graph of a section through a g;nnetophyle and younu sp. i uphyte. 

 The root is already protruded from the under >ide of the unmc- 

 minm ; s = snspensor ; / = stem-tip ; /=tirst 



