XII 



LEPTOSPORANGIAT^ HETEROSFORE^ 



391 



divided into an acroscopic and basiscopic cell, and these are further 

 divided into a dorsal and lateral cell in the upper ones, into a 

 ventral and lateral one in the lower. The leaves arise from one 

 of the dorsal cells, which may be either acroscopic or basiscopic. 



Fig. 201. — AzollaJilictdoidesiXj^m..'). A, Vertical longitudinal section of the stem apex, X6oo; r, 

 mother cell of a root ; B, three successive transverse sections just back of the apex ; m, the 

 median wall; L, mother cell of a leaf, x6oo; C, single lobe of a j'oung sterile leaf, X 600 ; D, 

 fertile leaf segments with two very young sporocarp rudiments, X 600 ; E, longitudinal section 

 of young macrosporangium, showing the young indusium (id), X 600 ; t, first tapetal cell ; F, 

 older macrosporangium completely surrounded by the indusium, X350 ; n, Anahcetia filaments. 



but is always constant on the same side of the shoot, so that 

 the two rows of leaves alternate. The lateral buds, which do 

 not seem to appear at definite intervals, arise from one of the 



