PILULARIA. 



[ 507 ] 



PINNULARIA. 



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, 



Fig. 579. 



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. 



Fig. 580. Fig. 583. 



Fig. 581. 



Fig. 582. 



Pilularia globulifera. 

 Fig. 579. Natural size. 



Fig. 580. An ovule-spore. Magnified 25 diameters. 

 Figs. 581 & 582. The same in germination. Magnified 25 diameters. 

 Fig. 583. Germinating spore more advanced. Magnified 10 diameters. 



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, consisting 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 arche- 

 gonium, and this becomes developed into a 

 new plant, within the substance of the pro- 

 thallium (fig. 582), sending out a leaf on 

 one side and an adventitious root on the 

 other, tangentally to the surface of the spore. 

 In this stage (fig. 583) the young plant, 

 with the remains of the spore, somewhat 

 resembles a germinating Monocotyledonous 

 seed. Finally, as the young plant increases 

 in size, the remnants of the spore-coat are 

 thrown off. 



BIBL. G. W. Bischoff, Krypt. Gewachse, 

 Rhizocarpeen, Nuremberg, 1828. pi. 8; Va- 

 lentine, Linnean Trans, xvii. ; Schleiden, 

 Grundzuge, 3 ed. ii. p. 104 (Principles, 

 p. 203); Nageli, Zeitschr.f. Wiss. Botanik. 



heft iii. & iv. p. 188 ( Ann. des Sc. nat. 3 ser. 

 ix. p. 99) ; Hofmeister, Vergleichend. Un- 

 tersuch. Leipsic, 1851. p. 103. pis. 21, 22; 

 Mettenius, Eeitr. z. Kenntn. des Rhizocarp. 

 Frankfort, 1846 ; Henfrey, Ann. Nat. Hist. 

 2 ser. ix. p. 447, Trans. Brit. Assoc. 1851. 

 p. 116. 



PINE-APPLE. See BROMELIACE.E. 



PINNULARIA, Ehr. A genus of Dia- 

 tomacea3. 



Char. Frustules single, free, longer than 

 broad ; front view linear or oblong ; valves 

 navicular, elliptical, lanceolate or oblong 

 (side view), with a median line and a nodule at 

 the centre and at each end, surface exhibit- 

 ing transverse or slightly radiating striae or 

 furrows. 



This genus differs from Navicula in 

 the stria3 not being resolvable into dots. 

 They are mostly distinct under ordinary 

 illumination. In some of the species they 

 are absent in the middle, leaving a transverse 

 clear space or band, resembling in appear- 

 ance the stauros of Stauroneis. 



Twenty-four British species (Smith). 



