406 



BOTANY 



PART II 



1|P 



widely-spread diseases known as Rusts. Their more varied spore- formation is a 



distinguishing feature as contrasted with the Ustilagineae. 



As in tlie latter order, the 

 basidia are not produced directly 

 on tlie mycelium but on the 

 germination of a special type of 

 spore, TELEUTOSPORES or winter 

 spores, which are characteristic 

 of all Uredineae. The teleuto- 

 spores arise in small clusters 

 beneath the epidermis of the 

 diseased leaf from tlie ends of 

 hyphae ; frequently two or more 

 form a short chain. They are 

 thick-walled resting-spores and 

 persist through the winter (Fig. 

 338, 1, ot). The group of spores 

 Tisually bursts through the 



Fir;. iZ\\.—Gy,niwspomn.(jium.>iararlaefijnne. A spermo- epidermis. At first the spores, 



gonium rupturing the epidermis of a leaf of Crataegus ; ]j|.g |.j,g ^gjjj^ ^^ ^jip mycelium 



w, spermatia ; B, sterile paraphyses. (Af'terBi-ACKMAX.) i • , i ,^ i 



which bears them, have two 



nuclei, Imt the nuclei fuse before the spore is ripe. 



In the germination of tlie teleutospore a basidium (promycelium) grows from 



Fio. 340. — Pw.nnia grambiis. Aeuidiuui on JJerhcris rulgaris : ep, epidermis of lower surfaceof leaf ; 

 m, intercellular niyeeliiini ;;), peridiuni ; .-■, chains of spores, (x 1-42.) 



each cell (Fig. 338, 2) ; it l)ecomes divided by a transverse septa into a row of four 

 cells from each of which a stcrigma bearing a single uninucleated basidiospore 

 (sporidiura) is produced. The sporidia ai-e dispersed by the wind and germinate 

 in tlie spring on the leaves of liost plants (which may be of the same or diffei-ent 



