228 



THE SPORE-PRODUCING ORGANS 



[CH. 



form a continuous flange (Fig. 224). Christ has also indicated a more com- 

 plete fusion in Ncphrolepis acutifolia,vj\\ere "coenosori," or ftisioit-sori, may 

 extend along the whole margin. Similar fusions of marginal sori, more or 



Fig. 224. Group of sori, which have become apparently intra-marginal by the upper in- 

 dusial lip simulating the rest of the leaf-surface. A = Saccolonia elegans, after von 

 Goebel; B = Microlepia platyphylla, after von Goebel ; C=Ncphrolepis acuta, after 

 Christ; D = Nephrolepis cordifolia, after Christ. 



less continuous, are seen also in Lindsaya\ there is a complete fusion of 

 marginal sori in L. sagittata, and lancea, the veins being linked together 

 distally by commissural arches (Fig. 225). But the most familiar cases are 

 those of the Pterideae and Blechneae. In the former the receptacle of the 

 sorus, which is continuous at or 

 near the margin of the leaf, is 

 traversed throughout its length 

 by a vascular tract parallel to 

 the margin. It is made up of the 

 endings of the veins, which are 

 linked together by arched com- 

 missures (Fig. 218, C, Z>). If a 

 section follows the vein outwards 

 the appearance is as though there 

 were a simple marginal sorus : 



Fig. 225. A single pinna of Lindsaya lancea, showing 

 the sori fused laterally to form an almost continuous 

 intra-marginal series. ( x 4.) 



but if it traverses the space between two veins it cuts the commissure only 

 (Fig. 220, C). Such structure is clearly that of a fusion-sorus. The physio- 

 logical advantage of linking up the distal ends of the veins is obvious, while 

 it gives added space for the accommodation of sporangia. 



The condition seen in the Blechneae is more complicated, and it illustrates 

 how plastic is the development of the sporophyll. These Ferns appear to 



