XIII.] MOULDS. 417 



formed by the wall, and present large central clear spaces, 

 or vacuoles. At intervals, transverse partitions, continuous 

 with the walls of the tube, divide it into elongated cells, 

 each of which contains a correspondingly elongated proto- 

 plasmic sac, or prh?iordial utricle. Each cell contains a 

 number of small nuclei, the presence of which can only be 

 detected by the use of staining reagents. Thus in Pe?ii- 

 cilliu7n we have our first example in the vegetable kingdom 

 of 7nultinucleate cells. The hyphae frequently branch, and, 

 in the crust, they are inextricably entangled with one 

 another ; but every hypha, with its branches, is quite dis- 

 tinct from every other. Those aerial hyphse which are 

 nearest the periphery of the crust end in simple rounded 

 extremities; but the others terminate in brushes of short 

 branches, and each of these branches, as it grows and 

 elongates, becomes divided by transverse constrictions into 

 a series of rounded spores arranged like a row of beads. 

 The spores formed in this manner are termed conidia, and 

 the hyphas bearing them are termed conidiophores. At the 

 free end of each filament of the brush the conidia become 

 very loosely adherent, and constitute the green powdery 

 matter to which reference has been made. Examined 

 separately, a conidium is seen to be a spherical body, com- 

 posed of a transparent sac, enclosing a minute mass of pro- 

 toplasm and a nucleus, in all essential respects similar to a 

 Torula. If sown in an appropriate medium, as for example 

 Pasteur's solution, with or without sugar, the comdtu7?i 

 germinates. Upon from one to four points of its surface an 

 elevation or bulging of the cell-wall and of its contained 

 protoplasm appears. This rapidly increases in length, and, 

 continually growing at its free end, gives rise to a hypha, so 

 that the young Penicillium assumes the form of a star, each 

 ray being a hypha. The hyphse elongate, while side branches 



