39<5 



VASCULAR CRYPTOGAMS. 



microsporangia arises, at least according to observations made on Pilularia, in the 

 following manner^: — If a microsporangium is about to be formed, each of the 

 mother-cells is broken up into four tetrahedral spores, which all develope into 

 microspores; in the macrosporangium, on the contrgjy, the mother-cells remain, 

 with one exception, undivided ; this one first of all divides in exactly the same 

 manner as the mother-cells of the microspores (Fig. 297, /) ; but only one of the 



four daughter-cells developes any further; 

 in the three others the formation of a 

 rough exospore is commenced covered 

 by an outer gelatinous layer ; this latter 

 soon becomes absorbed, the three abortive 

 spores are arrested in their development 

 (Fig. 297, //, ///), while the fourth at 

 once increases rapidly in size, and grows 

 into an ovoid sac at first thin-walled, 

 exceeding several hundredfold the size 

 of the three sister-cells. The remainder 

 of these abortive sister-cells usually remain 

 for some considerable time shrivelled up 

 and hanging to the apex of the ma- 

 crospore, and may even sometimes be 

 found on it when ripe. The macrospore 

 of Pilularia is at first entirely clothed 

 with one coat, but after it has attained 

 about one-third of its ultimate length, 

 it has two, an inner compact brown and 

 an outer hyaline one. While the spore 

 is growing, this hyaline coat forms a 

 dome- shaped projection at the apex of 

 the spore (Fig. 298 d') and at the same 

 time a third coat (c) is formed, which is 

 very evidently composed of radiating 

 prisms. These prisms are short at the 

 lower part of the spore, but much longer 

 below its apex, and there form a collar, 

 surrounding the dome-shaped projection 

 (d') already mentioned. On the latter 

 also appears a thin gelatinous layer with 

 a prismatic structure, which however is not very clear. Finally, when the spore 

 has attained almost its full development, it becomes surrounded with a fourth 



Fig. 296. — Development of the sporangium oi Pilularia 

 globulifera, all the figures in optical longitudinal section ; 

 c central cell or primary mother-cell of the spores, ; s»i 

 mother-cells of the spores (xsso). 



^ On the corresponding processes in Marsilea, see Russow, I. c — Russow takes the opportunity 

 of objecting that in the formation of the spores of the higher Cryptogams I do not assume the 

 existence of special mother-cells. I can only reply that I never anywhere assume their existence, 

 principally because the idea of a special mother-cell is always superfluous, and is not in accordance 

 with our present cell-theory. 



