230 THIRD GROUP. — VASCULAR CRYPTOGAMS. 



single cell'. The protoplasm in each of the two cells of the antheridium contracts 

 and by repeated bipartition divides into four roundish primordial cells (spermatocytes), 

 each of which produces a spermatozoid, a small portion of the contents remaining 

 unused in each cell. The walls of the antheridial cells split by transverse fissures into 

 valves which open and release the spermatozoids. The body of the spermatozoid is 

 spirally coiled and lies in (?) a vesicle which according to Pringsheim it does not part 

 with during its time of active movement, but which it certainly loses eventually. 



The course of proceeding is exactly the same in the Marsiliaceae {Marsih'a and 

 Pilidarid). There too the microspore divides into three cells, one of which is very 

 small and represents the prothallium, while the two others together form the an- 

 theridium ; but the entire group of cells remains enclosed in the microspore till the 

 formation of the spermatozoids, and the microspores themselves are free and not as 

 in the Salviniaceae still enclosed in the microsporangium. The protoplasm of each 

 of the two antheridial cells divides by repeated bipartition into sixteen spermatozoid- 

 mother-cells (spermatocytes). The spermatozoids are formed as in the Ferns, that is, 

 mainly from the nucleus of the mother-cells. The portion of the contents of the 

 mother-cell which is not employed in their formation appears when the spermatozoid 

 issues from the cell as a vesicle formed of the unused protoplasm with its starch- 

 granules. In Pilulan'a, where the spermatozoid is a thread coiled four or five times, 

 this vesicle remains behind in the mother-cell ; in Marsilia on the contrary it adheres 

 to the posterior coils of the spermatozoid which forms from twelve to thirteen 

 spiral coils, and is often carried about with it for some time during its period of 

 active movement, but is at length brushed away. When the spermatozoids are 

 developed in the mother-cells, the exosporium is ruptured at the apex and the endo- 

 sporium swells and protrudes as a hyaline vesicle, which ultimately bursts and 

 releases the spermatozoids (Fig. 183). 



The development of the female prothallia in the macrospores is most simple in 

 the Marsiliaceae. The macrospores are nearly ovoid in form and have a roundish 

 papilla at their apex. The lenticular space inside the papilla is filled with finely 

 granular protoplasm, while the lower and much larger portion of the macrospore 

 contains chiefly large grains of starch with oil-drops, albuminoid bodies and other 

 substances. In germination a membrane forms round the lenticular mass of protoplasm 

 in the apical papilla. Divisions^ in this protoplasm give rise to an upper and a 

 lower layer of cells, and the middle cell of the upper layer is the mother-cell of the 

 archegonium which developes in the same way as in the homosporous Ferns. The 

 prothallium contains chlorophyll, which according to Arcangeli is found also in 

 macrospores that have been kept from the light. The archegonium then makes its 

 appearance completely sunk in the prothallium, which in Marsilia therefore appears 

 to form a part of the venter of the archegonium (see Fig. 185). The reserve-material 

 stored up in the lower, larger portion of the macrospore which does not contribute 

 to the formation of the prothallium is subsequently used by the latter for its support. 



That a prothallium is present as a distinct structure and that it is not entirely 



I 



^ Even among the homosporous Fems prothallia bearing antheridia are often found in an 

 imperfect state of development and in the form of a few-celled filament. 



^ According to Arcangeli, !oc. cit. Hanstein gives a somewhat different account of the procesb 

 in Marsilia. 



