PILOPHOEON. 



[ 593 ] 



PILrLARIA. 



ing some resemblance iu their structm-e to 

 Botrijdium among the Algse. The plants 

 Lave a stolon iferous creeping mycelium, 

 from wlueh arise fertile pedicels, each cut 

 off from the mycelium by a septum; the 

 upper part of the pedicel expands into the 

 ■vesicle, which also becomes shut oft" by a 

 septum ; in the vesicle or peridiole, spores 

 are next developed by free-cell formation, 

 and at the same time' the septum becomes 

 pushed up into its interior (as in Mucoe) 

 to form a columella, which ultimately causes 

 the vesicular peridiole to split off by a cir- 

 cumscissile dehiscence just above the sep- 

 tum ; it is thrown off" with elasticity, en- 

 closing the spores. Tlie development of 

 P. crystaUiiius has been studied by Colin and 

 Bail.' They hud the germinating spore to 

 produce a creeping unicellular mycelial por- 

 tion, and next a fruit-pedicel, which soon 

 has the peridiole separated by a septum ; 

 thus, in its simplest form, this plant consists 

 of only three cells ; subsequently it becomes 

 complex by the root-cell or mycelium pro- 

 ducing numerous stolons. P. crystallinus is 

 yellowish at first, the peridiole finally black. 

 P. roridus, Bolt., a doubtful species, is smaller 

 and more slender than the last, having an 

 elongated filiform stem. 



Bjbl. Berk. Br. Fl. ii. pt. 2. 231 ; Fries, 

 Sum. Vef/et. 487 ; Cohn, Kova Acta, xxiii. 

 492 ; Bail, Hot, Zeit. xiii. C30 ; Currey, J. 

 Liim. Sue. Botany, i. 162. 



PILOPH'ORUN,Tuck.— Agenus of Cla- 

 douiei (Liclienaceous Lichens ). P. Jihula, 

 on wet rocks, rare. ( Leighton, Lich. Fl. 69.) 

 PILOT'PJCHUM, Pal. de Beauv.— A 

 genus of Hypnoid Mosses, including some 

 Fontincdes of authors. 



Pilotrichum antipyreticum, C. Mull.= 

 Fontinalis antipyrelica, L. 



P. squamosum, C. Miill. = F. squamosa, 

 L. 



P. ciIi(itu7n,C MiiYl.^ Anoecfaiiffiion cilia- 

 tum, Brid., var. y. striafum = A. cUiutum, 

 Wilson. 



P. hcteromaUum, P. d. ^.—Daltoniaheie- 

 7'otiialla, 11. and T, 



PILULA'EIA, L.— A genus of Marsile- 

 aceous Plants, containing the only British 

 representative of the order — P. glohuUfera 

 (fig. 574). Tliis is an iuconspicuous plant 

 growing in mud at the edges of or in pools, 

 having a filiform creeping stem, bearing 

 erect filiform pTeen leaves and delicate ad- 

 ventitious roots, and producing shortly- 

 stalked globular spore-fruits, about the size 

 of a pepper-corn. The anatomical structure 



of the stem and leaves is simple : they are 

 clothed with an epidermis possessing sto- 

 mata ; and a cross section both of the stem 

 and the leaves exhibits a central vascular 

 bundle (of spiral vessels) surrounded by a 

 sheath of brownish cells, while in the deli- 

 cate cellular tissue intervening between the 

 central bundle and the epidermis stands a 

 circle of air-passages separated from each 

 other by simple radiating cellular septa. 



Fig. 572. 



Fig. 573. 



Pilularia globulifera. 



Fig. 572. h. vertical section of a spore-fruic. Magn. 

 .5 diameters. 



Fig .37-3. Transverse section of a spore-fruit. Magn. 

 b diameters. 



The spore-fruits are liollow cases with an 

 oiiter tough cellular coat, and an inner more 

 delicate coat dijipiuginat four perpendicular 

 lines, as far as the centre, so as to form 

 dissepiments dividing the fruit into four 

 chambers (fiffs. 572, 573) ; up the centre of 

 the outer wall of each chamber runs a raised 

 ridge, a kind of placenta, whence arise the 

 sporanges or thecce (fig. 573). These are 

 pear-shaped sacs composed of a very deli- 

 cate cellular membrane. Those in the upper 

 part of each chamber contain a number of 

 minute globular bodies (microspores), re- 

 sembhng pollen-grains, immersed in a gela- 

 tinous liquid. The sacs in the lower part 

 of the chamber contain only one body or 

 spore (macrospore) of very peculiar firm ; 

 it nearly fills the theca, is somewhat oval, 

 and possesses several coats. 



In the development of the spores the 

 small spores are developed in the usual way, 

 by the formation of parent cells in the 

 theca, each subsequently producing four 

 spores. In the thecfB which have the single 

 large spore, a number of parent cells are 

 origiually produced ; and these become 

 divided into four chambers by septa ; but 

 then all but one of these decay. This pro- 

 duces four spores; but out of these four, 

 only one attains ]ierfect development, the 

 rest being subsequently dissolved and ab- 

 sorbed to make room for the solitary large 

 spore. The two kinds of spore in Pilularia 



