EMBRYOLOGY 465 



The prothallus throughout the ^Ophioglossaceae is subterranean, and 

 without chlorophyll, excepting some traces observed by Campbell in the 

 early 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 Botrychium its form is 

 that of a flattened cake, with the slowly growing apex in a lateral position : 

 but in Ophioglossum 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 Ophioglossum, 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 Ophioglossum 

 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. vulgatum, 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. Zeit., 1904, and Flora, 1906 ; Lyon, Bot. Gaz., Dec., 1905; and 

 of Campbell, Ann. Jard. Bot., Buitenzorg, 1907, p. 138. 

 l Zu-., p. 171. 



2 G 



