LYCOPSIDA 63 



surface living. In the latter species, the neck is very short 

 e.g. Lycopodium cernuum (Fig. lol), and there may be just 

 a single canal cell, apart from the ventral canal cell. At the 

 other extreme, the number of canal cells may be as high as 

 fourteen in L. complanatum (in the Clavata subsection), 

 while L. selago is intermediate, with about seven. Various 

 stages in the development of L. clavatum are illustrated in 

 Figs. loJ-N. At maturity all the canal cells break down and 

 part of the neck may also wither (Fig. loO). The anthero- 

 zoids are pear-shaped and swim by means of two flagella 

 at the anterior end, attracted chemotactically by citric acid 

 diffusing from the archegonium.^* 



The orientation of the embryo in Lycopodium is endo- 

 scopic and this is determined at the first division of the 

 zygote, with the laying down of a cross wall in a plane at 

 right angles to the axis of the archegonium (Fig. loU). The 

 outermost cell, called the 'suspensor', undergoes no further 

 divisions, but the innermost cell gives rise to two tiers of four 

 cells, called the 'hypobasal' and 'epibasal' regions respectively 

 (Fig. loW). It is from the epibasal (innermost) tier that the 

 young plant is ultimately derived, by further divisions. The 

 hypobasal region remains small in some species, and in 

 others it swells up into a structure commonly called a *foot'. 

 L. clavatum is an example of the latter and various stages are 

 illustrated in Figs. loU-Z. In Fig. loX, the three regions of 

 the embryo are clearly demarcated (the suspensor cell, *s' ; 

 the middle hypobasal region, already beginning to swell 

 into a foot, 'f; the epibasal region with a stem apex, *x', 

 becoming organized), and the axis of the embryo has bent 

 through a right angle. This bending of the axis proceeds 

 further in Fig. loY and is completed in Fig. loZ, where, by 

 turning through two right angles, the stem apex is pointing 

 vertically upwards. The first root, 'r', is seen to be a lateral 

 organ, not forming part of the axis of the embryo, as indeed 

 is the case in all pteridophytes : not until the level of the seed 

 plants does the root (radicle) form part of the embryonic 



