EMBRYOGENESIS IN i: U S POR ANGI ATE FERNS 137 



saprophytic underground prolhallus, consists of a massive foot and a 

 primary root. In B. huiaria the first leaf is insignificant and non- 

 vasculated, and several similar rudimentary leaves are formed before 

 the first green leaf appears above ground. This requires several years. 

 In both B. simplex and B. lunar ia the shoot apex develops slowly as 

 compared with the root system, but in the former species the first leaf 

 is better developed and the second leaf appears above ground (Bruch- 

 mann, 1906). 



Campbell (1911) has given some important comparative data 

 relating to the early development in different species. In B. virginianum, 

 there is a considerable enlargement and some elongation of the zygote 

 before the first partition wall is formed; in B. limaria this elongation 

 is considerably less marked; while in B. ohUquiim the zygote becomes 

 much elongated before the first division, Fig. 31g, h. Whether 

 directly or indirectly, these diff'erences reflect differences in the genetical 

 systems of the three species. The basal wall in B. virginiamim divides 

 the elongated zygote unequally into a larger epibasal and a smaller 

 hypobasal segment. Indeed, at a first glance, it appears as if a sus- 

 pensor might be present (Campbell, 1911). However, Campbell (1940) 

 states that this species has no suspensor, the embryogeny being like 

 that of B. simplex. 



In B. obliqimm, Fig. 31g, h, a suspensor is present, the embryogeny 

 is endoscopic and the embryo proper develops from the densely proto- 

 plasmic terminal cell. This cell divides by a wall of variable position, 

 the hypobasal cell (adjacent to the suspensor) giving rise to a large foot, 

 while the distal or epibasal cell gives rise to a somewhat inconspicuous 

 superficial shoot apex and a bulky first leaf. Some time later the first 

 root is formed endogenously near the centre of the embryo. As it 

 grows it penetrates the foot. A vascular strand extends from the first 

 leaf into this root. Root elongation is rapid, keeping pace with the 

 growth of the first leaf, so that, according to Campbell (1940), 'the 

 young sporophyte has a definite bipolar structure.' The first leaf 

 eventually appears above ground, (^^e Campbell, 1911, 1940; Lyon, 

 1905; Bower, 1908, 1935.) An initial cell is present in the shoot apex. 

 No vascular tissue is discernible below the shoot apex, A massive 

 sheath develops at the base of the first leaf and encloses the apical 

 meristem and the second leaf which is formed on the flank of the 

 meristem. The vascular strand of the second leaf joins that already 

 present, i.e. the vascular system in the shoot in Botrychium appears to 

 be entirely of foliar origin. 



In the specialised but evidently related group of organisms that 

 constitute the genus Botrychium, it is a matter of considerable interest 

 that a suspensor is present in some species but not in others. Moreover, 



