274 



PLANT STUDIES 



dew, Microsphcera^ grows on lilac leaves, which nearly al- 

 ways show the whitish covering after maturity (Fig. 241). 

 The branching hyphae show numerous partition walls, and 

 are not coenocytic as in the Phycomycetes. Small disk-like 

 haustoria penetrate into the superficial cells of the host, 

 anchoring the mycelium and absorbing the cell contents. 



Sporophores arise, which form asexual spores in a pe- 

 culiar way. The end of the sporophore rounds off, almost 

 separating itself from the part below, and becomes a spore 

 or spore-like body. Below this another organizes in the 



same way, then another, until 

 a chain of spores is developed, 

 easily broken apart and scat- 

 tered by the Avind. Falling 

 upon other suitable leaves, 

 they germinate and form new 

 mycelia, enabling the fungus 

 to spread rapidly. This meth- 

 od of cutting a branch into 

 sections to form spores is 

 called abstriction^ and the 

 spores formed in this way 

 are called conidia^ or conidi' 

 ospores (Fig. 243, B). 



At certain times the myce- 

 lium develops special branches 

 which develo^J sex organs, but 

 they are seldom seen and may 

 not always occur. An oogo- 

 nium and an antheridium, of 

 the usual forms, but probably 

 without organizing gametes, 

 come into contact, and as a 

 structure is developed — the ascocarp^ 

 spore fruit." These ascocarps ap- 



FiG. 241. Lilac leaf covered with mil- 

 dew {Microsjyhoera), the shaded re- 

 gions representing the mycelium, 

 and the black dots the ascocarps.— 

 S. M. Coulter. 



result an elaborate 



sometimes called the " 



pear on the lilac leaves as minute dark dots, each one being 



