EMBRYOLOGY 465 
The prothallus throughout the. Ophioglossaceae is subterranean, and 
without chlorophyll, excepting some traces observed by Campbell in the 
éarly germination of Botrychium, while Mettenius, and later Campbell, have 
noted in O. pedunculosum that some branches of the thallus extended 
above ground, and became flattened and green. But with such exceptions 
as these the gametophyte is massive and colourless, and is buried under- 
ground. Its nutrition is holosaprophytic, with an endophytic mycorhiza, 
which is located especially in the lower region. In Bofrychium its form is 
that of a flattened cake, with the slowly growing apex in a lateral position : 
but in Ophieglossum and Helminthostachys there is a definite apical growth 
associated with the formation of one or more upward or lateral conical 
processes, and it is upon these that the sexual organs are borne. In 
Botrychium they appear upon the surface of the cake, where the mycorhiza 
is absent. The antheridia are deeply sunk in the tissue of the gameto- 
phyte: the archegonia, which have the early segmentation as in Ferns, 
are deeply sunk in Op/zoglossum, but in Botrychium and Helminthostachys 
the neck of the archegonium is elongated and projecting. The orientation 
of the archegonia does not appear to be constant, but in Ophzoglossum 
and Helminthostachys its axis appears to be horizontal, while in Botrychium 
it is oblique or vertical. The spermatozoids are spirally coiled, and bear 
numerous cilia. 
The development of the embryo of the Ophioglossaceae follows slowly 
on fertilisation, and shows peculiarities which may be held as concomitant 
on the subterranean habit, while the mycorhizic state may affect not only 
the prothallus, but in some cases the young sporophyte also. The most 
marked peculiarity is the delay in the actual growth of the apical bud, 
while there is a very precocious development of the root-system. Also, 
it will be seen that there is considerable variety in detail in the different 
representatives of the family, and even within the generic limits. This 
will make it desirable to describe them separately. 
In most species of Ophioglossum fertilisation seems to be of rare 
occurrence, and few embryos have therefore been available for study. The 
first division of the zygote is transverse to the axis of the archegonium: 
though Campbell specially .points out that it is not regularly so in O. 
pendulum’: this first segmentation separates the epibasal: from the hypo- 
basal region; but it has been difficult to follow the details of further 
segmentation owing to the scanty material, and reference of the parts to 
any definite relation to the initial cleavages is made specially uncertain 
by the fact that the embryo attains considerable size before any differen- 
tiation occurs (Fig. 260). Bruchmann states, however, for O. vwlgatum, that 
the hypobasal half gives rise to the first root and the foot; the latter is 
1905; Jeffrey, Gametophyte of Botrychium, Toronto, 1898; Lang, Ann. of Bot., xvi, 
1902; Bruchmann, Bot. Zedt., 1904, and Flora, 1906 ; Lyon, Bot. Gaz., Dec., 1905; and 
of Campbell, Azz. Jard. Bot., Buitenzorg, 1907, p. 138. 
1Zie, p. 171. 
2G 
