290 BOTANICAL GAZETTE [October 



into cells, rather than of a process of progressive cleavage; but 

 continuous observation of the successive stages of spore formation 

 affords no evidence in support of this assumption. Moreover, in 

 starved sporangia only partially filled with protoplasm the spores 

 when formed are more separate, and on swelling do not become 

 closely pressed together. Consequently, only an incomplete union 

 of the walls takes place (fig. 2); and the spores become rounded 

 off to a greater degree, so that the resultant structure is more 

 easily understood than the "cell-net" condition in the densely 

 filled sporangia. It is of interest to note that Zopf (12, pi. j, 

 Jig. 11) also figures a similar condition in D. carpophorus. This 

 union of the walls in the sporangium increases the mechanical 

 strength of the structure; and in consequence the final swelling 

 of the spores is resisted, and they do not burst out of the sporan- 

 gium, even though it becomes swollen and bulged. Frequently, 

 however, the swelling of the spores, combined with the outward 

 bulging of the terminal wall of the sporangiophore, is sufficient 

 to rupture the sporangial wall at the base (fig. 19), and the sporan- 

 gium is abjointed as a whole. This occurs quite commonly even 

 in vigorous cultures, as vON Minden (8) has observed, and does 

 not appear to be the result of degeneration and senescence, as 

 Leitgeb (6) and Fischer (4) have stated. 



Renewal of the sporangia is effected by cymose branching 

 (fig. 2), and by their formation in basipetal succession (fig. i). 

 The first method has been regarded as characteristic of D. mono- 

 sporus, and the second as typical of D. Magnusii; but the regular 

 occurrence of both methods in our form and even in D. Magnusii, 

 according to von Minden, would indicate that these characters 

 are not specific. 



In their subsequent development the sporangiospores within 

 the indehiscent Dictyuchus sporangium may either emit zoospores 

 or give rise to hyphae of germination. Since Leitgeb's original 

 description of these processes is quite detailed, only additional or 

 significant points need be mentioned here. The emergence of the 

 zoospore from the sporangiospore, although described at length 

 by this author, is only scantily figured. The accompanying draw- 

 ings (figs. 3-9), therefore, have been made to illustrate this process. 



