PETCOPHTTA. 



145 



pearing like an extension of the hypha, then called the 

 columella {G, a). The protoplasm in the enlarged termi- 

 nal cell (J) divides into a large number of minute masses, 

 each of which surrounds itself with a cell- wall; these little 





Fig. 75.— Diagrams showing mode of growth of the spore-case of Mucor 

 mucedo. ^, very young stage ; B, somewhat later ; C, spore-case with ripe 

 spores, a in all the figures represents the partition-wall between the last 

 cell of the filament and the spore-case, &. 



cells are the spores, and the large mother-cell is now a 

 spore-case, or sporangium. 



258. The spores are set free in different ways : in some 

 cases the wall of the spore-case is entirely absorbed by the 

 time the spores are mature; in other cases only portions 

 of the wall are absorbed, producing fissures of various kinds. 

 The spores germinate readily when on or in a substance 

 capable of nourishing them, by sending out one or two 

 hyphge, which soon branch and give rise to a mycelium. 

 Spores may, if kept dry, retain their vitality for months. 



259. Sexual reproduction takes place after the produc- 

 tion of asexual spores. Two hyphse, in the air or within 

 the nutritive medium, come near each other, and send out 

 small branches, which come in contact with each other {a, 

 Fig. 76); these elongate and become club-shaped, and at 

 the same time they become more closely united to each 

 other at their larger extremities (5) ; a little later a trans- 

 verse partition forms in each at a little distance from their 

 place of union (c); the wall separating the new terminal 



