412 



General Botany 



The method of spore formation is quite simple. The upright 

 hyphae of the blue mold branch several times near the end. In 



this way a broom-like tuft is formed, 

 the branches of which terminate in 

 rows of spores (conidia). In the green 

 mold numerous branches arise at the 

 enlarged ends of the upright hyphae, 

 forming a globular mass of spores. 



Under certain conditions these fungi 

 may form round, capsule-like fruiting 

 bodies in the material on which they 

 are growing. Within a capsule is a 

 group of sacs (sporangia), each of 

 which contains eight spores. It is the 

 presence of these sacs and sac spores 

 that show the relationship of the blue 

 and green molds to the sac fungi rather 

 than to the bread molds. 



The powdery mildews. Closely 

 related to the green mold are the 

 powdery mildews which form con- 

 spicuous white cobwebby patches 



Fig. 253. A, vertical section of OU the IcaVCS of rOSCS, lilaCS, willoWS, 



an ascomycete Pcsfca; B, en- dandelions, and many other plants in 



larged view of fruiting layer, 



showing asci- and ascospores. late summcr. They too produce m- 

 {After Frank.) numerable spores from simple upright 



hyphae. These form the dust-like powder which suggested their 

 common name. Late in the season, after the union of two 

 hyphae, larger fruiting bodies may be formed, and within them 

 groups of sacs and sac spores. These appear on the leaves as 

 black dots and usually have a number of appendages. The 

 powdery mildews are external parasites and derive their food 

 from the epidermal cells of the leaves or stems of the host 

 plant. 



