4i6 



BOTANY OF THE LIVING PLANT 



branches {pro gametangia), either of the same mycelium (Sporodinia), 

 or of distinct myceiia [Mucor stolonifer, and other Mucors), growing 

 towards one another, meet at their apices (Fig. 314). From the end of 

 each a conjugating cell or gaynetangium containing protoplasm with 



many nuclei is cut off by a trans- 

 verse septum from the basal sus- 

 pensor. Their apices flatten, and 

 the gametangia fuse, the wall 

 separating them being absorbed. 

 Many nuclei are involved ; these 

 fuse in pairs and the result on 

 maturation is a zygospore (Fig. 

 314, 4). The large protoplast is 

 stored with nutritive material, 

 while the outer wall thickens, 

 often forming characteristic bosses 

 externally (Fig. 314, 3, 4)- In 

 this condition the zygospore may 

 undergo a period of rest, and is 

 resistant to unfavourable con- 

 ditions. But suitable conditions 

 induce germination, and they de- 

 termine what follows. Sometimes 

 there is a formation of a vegetative 

 mycelium, sometimes, as in Fig. 

 314, 5, an immediate formation of 



Mucor Mucedo. Different stages in the forma- a sporangium I the Spores prO- 

 tion and germination of the zygospore, i =two . , « i r 



progametangia in contact. 2 =septation of the duced in the latter are the tirSt 

 two gametangia. 3 = more advanced stage ; the 



conjugating cells are still distinct from one stage of the new gametophyte. 

 another. 4 =ripe zygospore (b) between the . 



suspensors (a). 5 =germinating zygospore with A remarkable fact IS the OCCUT- 



germ-tube bearing a sporangium. (After Brefeld.) ' 



(1-4x225; 5 x circa 60.) (From v. Tavei.) rence in some Mucors 01 Azygo- 



(From Strasburger.) , 



spores," that is, bodies that re- 

 semble zygospores in their structure and covering, but are produced 

 without any fusion. 



According to their power and readiness for conjugation the Mucorales 

 have been divided into two groups. The Homothallic, which form zygospores 

 on two branches of the same mycelium, so that by sowing a single spore 

 zygospores may be obtained. This is seen in Sporodinia, in which the zygo- 

 spores may often be obtained in the open in autumn. Others are called 

 Heterothallic, where the presence of two individuals of two different types 

 is necessary for the production of zygospores (Rhizopus, Mucor, Phycomyces) 

 These types are distinguished as + and - , rather than as male and female, 



Fig. 314. 



