PENICILLIUM. 



[ 496 ] 



PERACANTHA. 



shown in figs. 15 and 16 of PI. 20. The 

 mycelium consists of interwoven articulated 

 filaments, most extensively ramified. The 

 spores appear whitish, yellowish, greenish, 

 or bluish, according to age : under the mi- 

 croscope, they appear opake when mature. 



So far there is little difficulty about the 

 history of these plants, and if the spores of 

 the above form are sown on a glass slide, 

 kept moist with an organic liquid, they will 

 germinate and ramify, and under favourable 

 circumstances bear thin penicillate tufts of 

 spores at points which emerge from the 

 nutrient liquid. But this same fructification 

 of P. glaucum presents itself invariably 

 under certain circumstances associated with 

 the vinegar-plant and the yeast-plant, toward 

 the close of the ordinary development of 

 these fungi. In common with most obser- 

 vers, we find that the exhaustion of the sac- 

 charine matrix of the vinegar-plant is fol- 

 lowed in all cases by the appearance of 

 crusts of Penicillium-moulA on the upper 

 surface, whence it would appear that the 

 vinegar-plant was only the mycelium of 

 Penicillium. It was asserted, moreover, 

 many years ago, by Turpin, that P. glaucum 

 is the last term of the growth both of the 

 true yeast-plant, Torula Cerevisice, and of 

 the milk-yeast, Oidium lactis. We have 

 found the gelatinous crusts of the vinegar- 

 plant to contain structures which represent 

 Torula and Oidium, and to grow like them ; 

 and we have also observed, in repeated expe- 

 riments, that beer allowed to stand until 

 sour, at first appears clothed with a whitish 

 mealy collection of minute vesicles, repre- 

 senting the ultimate stage of Torula, and 

 subsequently this gradually gave place to 

 gelatinous matter, which at length covered 

 the whole surface with a tough film, and 

 fruited as Penicillium glaucum. Hence it 

 would appear that the yeast-fungus also is 

 merely a vegetative form of Penicillium 

 developed under peculiar conditions. More 

 is said on this point under VINEGAR-PLANT 

 and YEAST. 



Several species are enumerated, and we 

 have given under the separate head of 

 COREMIUM a form which is now regarded 

 as merely a confluent growth of Penicillium, 

 producing a compound pedicel. 



1. P. glaucum, Grev. Mycelial filaments 

 form a crust-like web, spores green or bluish. 

 Greville, Sc. Crypt. Fl. pi. 58. fig. 1. P. 

 crust aceum, Fries. Extremely common. 



2. P. candidum, Lk. Mycelial filaments 

 woven together, spores white. (Distinct ?) 



3. P. sparsum, Grev. Mycelium lax, 

 spores white. -Sc. Crypt. Fl. pi. 58. fig. 2. 

 Perhaps not different from the last. 



^ . P. fasciculatum, Sommer. Mycelium 

 scarcely developed, filaments all fertile, 

 trifid at the apex, spores glaucescent. 



5. P. subtile, Berk. Extremely minute, 

 mycelium creeping, fertile filaments erect, 

 simple or ternate ; chains of spores few, 

 spores broadly elliptical. Ann. Nat. Hist. 

 vi. pi. 14. fig. 25. 



6. P. roseum, Lk. Mycelium effused ; 

 fertile filaments slightly branched, spores 

 rose-colour. 



BIBL. Berk. Hook. Brit. FL ii. pt. 2. 

 p. 344 ; Ann. Nat. Hist. i. p. 262, vi. p. 437, 

 ser. vii. p. 102; Greville, loc. cit.; Fries, 

 Syst. Myc. iii. 407, Summa Vegetabilium, 

 p. 489. See also under YEAST and VI- 

 NEGAR-PLANT. 



PENIUM, Brelj. A genus of Desmidi- 

 acese. 



Char. Cells single, entire, elongated, 

 straight, and slightly or not at all constricted 

 in the middle. 



Sporangia round or quadrangular, smooth, 

 not spinous. 



At each end of the cells is a rounded 

 space containing moving molecules. 



Eight British species (Ralfs). 



P. Erebissonii (PI. 10. fig. 36). Cells 

 smooth, cylindrical, ends rounded, transverse 

 median band inconspicuous. Length 1-640 

 to 1-400". 



Common. Sporangium at first quadrate, 

 but finally orbicular ; conjugating cells per- 

 sistent, or remaining permanently attached 

 to the sporangium. 



P. margaritactum (PI. 10. fig. 37. empty 

 cell). Cells cylindrical or fusiform, with 

 rounded-truncate ends, and covered with 

 pearly granules in longitudinal rows. Length 

 1-160". 



BIBL. Ralfs, Brit. Desmid. p. 148. 



PENTASTERIAS, Ehr. (Desmidiacese). 

 The two British species are referred to 

 Staurastrum. 



PERACANTHA, Baird. A genus of En- 

 tomostraca, of the order Cladocera and family 

 Lynceidae. 



Char. Side view of shell oval, the lower 

 and posterior portion with an acute projec- 

 tion directed backwards and upwards, and, 

 as well as the upper extremity of the anterior 

 margin, beset with strong hooked spines ; 

 beak sharp, curved downwards. 



P. truncata (PI. 14. fig. 31). Superior 

 antenna; conical ; inferior short, the anterior 



