. A manual of botany. Botany. 148 MANUAL OF BOTANY >a through the wall of the sporangium. It then forms a septum at the end, cutting off a terminal cell which later divides into two. The tube constitutes the prothallium, and its two end cells after further divisions form a rudimentary antheridium, in which are produced four antherozoids {fig- 906). \¥henthe antherozoids are mature, the antheridium ruptures as in other cases, and the antherozoids, each in its mother-cell, escape into the water. Only part of the protoplasm of the mother-cell is used in the formation of the antherozoid, as in
. A manual of botany. Botany. 148 MANUAL OF BOTANY >a through the wall of the sporangium. It then forms a septum at the end, cutting off a terminal cell which later divides into two. The tube constitutes the prothallium, and its two end cells after further divisions form a rudimentary antheridium, in which are produced four antherozoids {fig- 906). \¥henthe antherozoids are mature, the antheridium ruptures as in other cases, and the antherozoids, each in its mother-cell, escape into the water. Only part of the protoplasm of the mother-cell is used in the formation of the antherozoid, as in the ferns. AzoUa produces a similar male gametophyte. In the Marsi- leacese the latter' is Pis- 906. formed within the microspore. 'The first division of the spore produces a small basal vegetative cell and a larger apical one, which forms an anthe- ridium. By successive divisions this comes to consist of eight cells surrounded by a pa- rietal layer or wall. The central cells pro- duce each four anthero^ zoids. Throughout the group the male pro- thallium is destitute of ohloroplastids. The formation of the female prothallium is a good deal alike in all the genera, showing small differences in the extent of its protrusion from the spore, from which it is never free. The macrospore begins to germinate before its coats rupture ; it first cuts off a small cell at its anterior end or apex, by a wall known as the diaphragm, which thus divides the spore into two. The small cell at the apex continues to divide, forming a small celled tissue which soon protrudes through the spore- coats, owing to the rupture of the latter. The emerging tissue develops chloroplastids and becomes green; it constitutes the prothallium. In Salvinia it is somewhat triangular in shape and bears two winged appendages (fig. 007). In the Marsileaces only a small part of it protrudes from the opening of the Fig. 906. Germination of mici'ospores of Salcinia. After Sachs. 1. The mass of spores putting out
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