PILULARIA. 



[ r,no ] 



PILULARIA. 



correspond to the two forms in Selaqi- 

 NBLLA and IsoETE.s, and to the pollen and 

 ovules of the Flowering Plants. They are 

 set free by the dehiscence of the spore-lriiit, 

 and lie at first inib.'dded in the jelly poured 

 out by the thecse. 



In this state the small spores resemble 

 pollen-grains, having au outer granular, and 

 an inner delicately membranous coat, — the 

 outer coat presenting ridges coi'respouding 

 to the points of contact in the parent cell. 

 When set free, tlie spores soon burst at 

 these ridges, and tlie inner coat is slightly 

 protruded ; this next bursts and discharges 

 a number of lontienlor cells, from each of 

 ■which escapes a ciliated spiral spermatozoid. 



The mature large spore-s (tig. 575) are of 



oval form, and have a thick outer gelati- 

 nous coat Ci)mpt)sedof prismatic cells stand- 

 ing perpendicularly on an inner glassy coat ; 

 the gelatinous coat is perforated at the 

 summit byafunnel-sha}3ed opening through 

 which protrudes a pyramidal elevation of the 

 second, glassy coat ; the last is lined by a 

 delicate internal coat containing protoplasm, 

 starch, oil-globules, &c. Soon after the 

 expulsion of the spore, cell-formation takes 

 place inside the pyramidal protrusion of the 

 outer coat, from the cell-contents of the 

 spoi-e. The glassy coat next splits at this 

 point into four teeth, and exposes the cellular 

 structure {protliallium), which increases in 

 size, and acquires a green colour. An 

 archegoniuni is next formed on this, con- 



Fig. 574. 



Fig. 575. 



Fig. 578. 



Fig. 576. 



Fig. 577. 



Pilularia globulifera. 



Fig. S"4. Natural size. 



Fi;;. 57o. An ovule spore. Magnified 25 diameters. 



Figs. 576 & 577. The same in germination. Magnified 25 diameters. 



Fig. 578. Germinating spore more advanced. Magnified 10 diameters. 



sisting of a cell (embryo-sac) lying in the 

 substance at the apex, with a canal Ijordered 

 by four papillose cells leading to it. A 

 spermatozoid fertilizes the free embryo-ceU 

 contained in the archegonium ; and this be- 

 comes developed into a new plant within 

 the substance of the prothallium (fig. 577), 

 sending out a leaf on one side and an ad- 

 ventitious root on the other, tangentially to 



the surface of the spore. In this stage 

 (fig. 578) the j'oung plant, with the remains 

 of the spore, somewhat resembles a germi- 

 nating Monocotyledonous seed. Finally, as 

 the young plant increases in size, the rem- 

 nants of the spore-coat are thrown off. 



BiBL. Valentine, Linn. Tr. xvii. ; Hof- 

 meister, Vergl. Unters.\9>5\,\0Z ; Henfrey, 

 Ann. N. H. 2. ix. 447 j Hanstein, Pilul. ^c. 



