THE VASCULAR CRYPTOGAMS 



17 



The whole sporangium continues to grow and its cells to 

 divide. At the stage shown in Fig. 9, A, it already has 

 a short stalk, and the arche- 

 sporium has given rise to a 

 many-celled tissue. 



Up to this point both 

 kinds of sporangia behave 

 exactly alike. The reader 

 will at once see that, thus 

 far, the development of the 

 young sporangium is in all A 

 respects similar to that of a 

 pollen-sac (compare Fig. 9, 

 A, with one of the four 

 pollen-sacs shown in Fig. 39, 

 A, in Part I. p. 110. It 

 is also evident that in the 

 youngest stages there is a 

 considerable resemblance to 

 an ovule at its first origin 

 (cf. Fig. 9, B, with Fig. 44, 

 1 or 2, in Part I. p. 121). 



Henceforth it will be 

 necessary to distinguish 

 between a microsporangium 

 and a megasporangium. We 

 will first describe the former. 



The divisions of the archesporial cells of a microspor- 

 angium give rise to a mass of spore-producing tissue, 

 each cell of which now rounds itself off and becomes a 

 spore mother -cell. Each of the spore mother-cells, lying 

 free within the cavity of the sporangium, next divides 

 into four, the division taking place exactly in the same 



2 



spinosa. A, 

 young microsporangium in 

 longitiidinal section ; t, tapetum; 

 a (darkly shaded), mass of 

 sporogenous cells derived from 

 archesporium. B, very young 

 megasporangium ; t, tapetum ; 

 a, archesporii 

 aporophyll. Magnified about 



I, ligule of 

 lified about 

 300 diameters. (After Goebel. ) 



