512 MOSSES AND FERNS chap. 



The Microspores and Male Prothallium 



The microspores of all species of Selaginella are small and 

 of the tetrahedral type. According to Belajeff (i) they may 

 show either a distinct perinium, or the latter is not clearly sepa- 

 rated from the exospore. The spores contain no chlorophyll, 

 but include much oil as well as solid granular contents. At the 

 time that the spores are shed each one has already divided into 

 two very unequal cells, a very small lenticular cell (Fig. 295, x) 

 and a much larger one which, as in Isoetes, becomes the single 

 antheridium. 



The first wall in the antheridium divides it into two equal 

 cells, each of which then divides into two others, a basal and 

 an apical cell. The latter divides twice more, forming three 

 segments, so that the young antheridium at this stage consists 

 of eight cells arranged in two symmetrical groups. Of the 

 three segments formed in each apical cell, the first and some- 

 times the second form periclinal walls, so that a central cell 

 (or two cells) is formed in each half of the antheridium, not 

 unlike what obtains in Marsilia, and the young antheridium 

 consists now of two (or four) central cells and eight peripheral 

 ones. Belajeff states that the cell walls do not show the cellu- 

 lose reaction, and that they are later absorbed. Where there are 

 four primary central cells, these by further divisions produce 

 a single cell-complex, which, after the disintegration of the per- 

 ipheral cell walls, floats free in the cavity of the spore. Where 

 but two primary central cells are formed, each produces a sepa- 

 rate hemispherical cell mass. Belajeff does not state the num- 

 ber of sperm cells formed. The spermatozoids (Fig. 295, G) 

 are extremely small and closely resemble those of many Bryo- 

 phytes, as well as Lycopodium. Like these they are always 

 biciliate. 



Miss Lyon (2) has given a very different account of the 

 male gametophyte in 5'. apus. She states that in this species the 

 cytoplasm of the germinating spore contains large vacuoles sepa- 

 rated by bands of cytoplasm, which radiate from the central 

 "generative" nucleus. The latter, with its envelope of proto- 

 plasm, then divides into "two cells," but how the membranes 

 about these free cells are formed is not stated. These two cells 

 give rise to the two masses of sperm-cells, and in the radiating 

 vacuoles are formed granular masses which, to judge from the 



