264 



GENERAL MORPHOLOGY OF PLANTS 



of short septate hyphae which are branched at the end several 

 times in a forked manner (fig. 224). The sacs or asci are some- 



Fig. 223. 



Fig. 222. 



Willow mildew; Fruit of willow mildew, showing hooked 



bit of mycelium appendages. Genus Uncinula. 



with erect comdio- other mildew 



phores bearing Figs. 223, 224. Perithecia (perithecium) c 



chains of conidui; of two powdery mildews, showing escape of P? n e ?' 



left asci containing the spores from the crushed Microsphaera. 



Fig. 224. 



Fruit body of an- 

 "th 



conidium at 

 germinating. 



fruit bodies. 



what elliptical in outline. Several are formed in each fruit body, 

 and may be seen by crushing the latter in water and examin- 

 ing with a microscope. Each ascus contains several spores. 

 Other genera of the powdery mildews have different kinds of 

 appendages. 



426. The sexual process in the powdery mildews. The 

 sexual organs are short branches of the mycelium, a sperm case 

 and an egg case. The processes here described occur in the 

 genus Sph&rotheca. These branches arise close together and 

 their ends come in contact. At the point of contact an opening 

 is dissolved through the walls. The sperm nucleus in the sperm 

 case moves into the egg case and fuses with the egg nucleus (figs. 

 225-226). The egg-case cell now grows .into a short branch of 

 five or six cells. In the last cell but one are two nuclei. These 

 fuse into one, and the cell grows out into a large globose cell, the 

 ascus. The nucleus now divides to form eight nuclei which 



