PILULARIA. 



[ 509 ] 



PILULARIA. 



correspond to the two forms in SELAGI- 

 NELLA and ISOETES, and to the pollen and 

 ovules of the Flowering Plants. They are 

 set free by the dehiscence of the spore-fruit, 

 and lie at tirst imbedded in the jelly poured 

 out by the thecae. 



In this state the small spores resemble 

 pollen-grains, having an outer granular, and 

 an inner delicately membranous coat, the 

 outer coat presenting ridges corresponding 

 to the points of contact in the parent cell. 

 When set free, the spores soon burst at 

 these ridges, and the inner coat is slightly 

 protruded ; this next bursts and discharges 

 a number of lenticular cells, from each of 

 which escapes a ciliated spiral spermatozoid. 



The mature large spores (fig. 575) are of 



Fig. 574. 



oval form, and have a thick outer gelati- 

 nous coat composed of prismatic cells stand- 

 ing perpendicularly on an inner glassy coat ; 

 the gelatinous coat is perforated at the 

 summit by a funnel-shaped 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 

 spore. The glassy coat next splits at this 

 point into four teeth, and exposes the cellular 

 structure (prothallium), which increases in 

 size, and acquires a green colour. An 

 archegonium is next formed on this, con- 



Fig. 575. 



Fig. 578. 



Fig. 57a 



Fig. 577. 



Pilularia globulifera. 



Fig. 574. Natural size. 



Fig. 575. 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. 



si sting of a cell (embryo-sac) lying in the 

 substance at the apex, with a canal bordered 

 by four papillose cells leading to it. A 

 spermatozoid fertilizes the free embryo-cell 

 contained in the archegonium ; and this be- 

 comes developed into a new plant within 

 the substance of the prothallmm (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 young 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. 1851, 103 ; Henfrey, 

 Ann. N. H. 2. ix. 447; Hanstein, Pilul. #c. 



