ABOUT THE MOLDS. 



245 



fungus. A mold that has caused great damage to grape-vines the 

 Oidium Tuckeri is an incompletely developed fungus. 



A whitish substance may be remarked on the leaves of lilacs near 

 the middle of the summer, which 

 might be regarded on superficial 

 observation as dust from the road. 

 It is also a mold. The microscope 

 shows it to be made up of very deli- 

 cate threads, similar to those of spi- 

 ders' webs. As these threads become 

 older, we may observe joined to them 

 a number of little spheroidal bodies, 

 some very small and white, others 

 larger and yellow, and others brown. 

 The white and yellow corpuscles are 

 young fruits of the fungus, and the 

 brown ones are ripened fruits. If 

 one of the last is put into a drop 

 of water and pressed between two 

 glasses for mounting microscopic 

 preparations, it will let escape some 

 small pyriform, transparent sacs, 

 each inclosing spores, the number 

 of which varies according to the 



species, but is definite for each species. The arrangement of these 

 spore-containing sacs (sporangia?) is shown by the vertical section (Fig. 

 4). The number of sporangice (b) contained in each of the fruits varies 

 in different species from one to twenty and more. 



Aside from every scientific consideration, a great interest is given 

 to these plants by the beauty of their ornamentation ; and they form 



choice objects for preparations. Around each receptacle may be seen 

 numerous appendages radiating in every direction, and generally un- 

 colored. In some genera these appendages are long and flaky, while 

 other genera have only six or eight of them in the form of short needles 



