i88 PENICILLIUM AND AGARICUS LESS. 



the strict sense, or a continuous multinucleate mass of 

 protoplasm not divided into cells ; in Penicillium it is a cell- 

 aggregate an accumulation of numerous cells all in organic 

 connection with one another. As the cells are arranged in 

 a single longitudinal series, Penicillium is. an example of a 

 linear aggregate. 



Each cell surrounded, as already described, by a wall 

 of cellulose : its protoplasm is more or less vacuolated (E, vac], 

 sometimes so much so as to form a mere thin layer within 

 the cell-wall, the whole interior of the cell being occupied by 

 one large vacuole. Recently, by staining with logwood, 

 numerous nuclei have been found, so that the Penicillium 

 cell, like an Opalina (p. 123) or a filament of Mucor or Vau- 

 cheria, is multinucleate. 



The submerged hyphae have the same structure, but it is 

 easier to find their actual ends than those of the mycelial 

 hyphae. The free extremity tapers to a blunt point where 

 the cellulose wall is thinner than elsewhere (see E). 



The aerial hyphae from the youngest (white) part of a 

 growth consist of unbranched filaments, but taken from a 

 part which is just beginning to turn blue they are found to 

 have a very characteristic appearance (F 1 F 4 ). Each sends 

 off from its distal or upper end a larger or smaller number of 

 branches which remain short and grow parallel to one 

 another : the primary branches (r 1 , F 2 ) form secondary ones 

 (F S ), and the secondary tertiary (F 4 ), so that the hypha finally 

 assumes the appearance of a little brush or pencil, or more 

 accurately of a minute cactus with thick-set forking branches. 

 The ultimate or distal branches are short cells called sterig- 

 mata (F 5 , sfg). 



Next, the ends of the sterigmata become constricted, 

 exactly as if a thread were tied round them and gradually 

 tightened (r 1 , F 6 ), the result being to separate the distal end 



