144 



OSMUNDACEAE 



[CH. 



from the very first, as appears from Fig. 433,^, in which two sporangia are 

 shown already differing in segmentation. The cells marked (x) do not 

 compose the whole outgrowth : adjoining cells contribute to it, so that strictly 

 speaking the whole sporangium is not referable in origin to a single cell: it 

 is not truly Leptosporangiate. How various the subsequent cleavages may 

 be will be seen from Fig. 433, A to B. A comparison of C and D also brings 

 out clearly the very great differences in bulk occasionally seen in sporangia of 

 the same age. The large cell in the centre divides usually by three anticlinal 

 walls corresponding to those seen in the usual Leptosporangiate type, though 



Fig. 433. Todea harbara Moore. A, small part of section of a 

 pinnule showing two young sporangia ( x , x ); j9, C,Z), examples 

 of variety of sporangial segmentation, as seen in vertical sections ; 

 E, older sporangia cut transversely, showing difference in 

 sporangia side by side ; F, vertical section of a sporangium of 

 like age, with square-based sporogenous cell; G, a similar 

 sporangium with tetrahedral sporogenous cell; H, /, vertical 

 and transverse sections of older sporangia. The central figures 

 show two unequal sporangial stalks in transverse section. 

 (All X 200.) 



the cell which remains in the middle may still be either truncate or pointed 

 at the base. But sometimes it appears that four lateral cells may be cut off 

 by anticlinal walls, as in the largest sporangium in E, thus occasionally 

 conforming to the Eusporangiate type. Then follows the periclinal division 

 to separate the cap-cell. The archesporial cell thus surrounded by tissue 

 which will form the sporangial wall undergoes further divisions to form the 

 tapetum (£", F). Where the archesporium is truncate at the base the cell 

 or cells below it take part in completing the tapetum (F). The division of 

 the tapetum follows into two, or partially into three layers {F to /) together 

 with the subdivision of the sporogenous cell to form the spore-mother-cells. 



