19^ MORPHOLOGY OF MEMBERS. 



row. Nodal cells occupying clearly-defined positions produce the leaves in the 

 order stated. This development furnishes no evidence that the leaves are formed 

 in spiral succession ; the bilateral structure of the stem shows rather that a 

 spiral construction is in this case altogether inadmissible. The same may be 

 shown to be the case in Marsilea, where the creeping stem bears on its upper 

 side two rows of leaves, while the under side forms roots; the leaves borne on 

 the upper side may in this case be united in the order of their age by a zigzag 



Fig. 151.— Diagram of a flower-stalk oi Fritillaria imperialis, showing the divergences of the first twenty-four foliage-leaves ; 

 the relative lengths of the internodes are indicated by the larger or smaller distances between the circles. 



line broken right and left, which does not anywhere touch the leafless under side 

 of the stem, and corresponds in its course to the bilateral structure of the stem. 

 The spiral construction appears also to be meaningless in all those cases where it 

 is indifferent whether the spiral be carried right or left. This is the case where the 

 members are placed in two rows, with a' constant divergence of \, and are thus 

 arranged alternately in two orthostichies lying exactly opposite to one another, as is 

 the case with the branchings of many thallomes {e.g, Stypocaulon, Fig. 108, p. 139), 

 the leaves of Grasses, the lateral shoots of the lime, elm, hazel, &c. In all these 



