MESOSPORES 13 



It is in the germination of the teleutospore, presently to be 

 described, that its most distinctive feature is to be found. The 

 chief function of teleutospores is to act as resting-spores, and 

 in the majority of cases they will not germinate until they 

 have passed through a period of quiescence ; in the present 

 instance this period is the winter, but it is not necessarily 

 always so. The resting-spore is primarily a device to tide over 

 an unfavourable period — whether of food-supply, moisture, 

 temperature, or resistance of host — without regard to season. 

 Some species, however, have teleutospores which can germinate 

 immediately, as in P. Malvacearum ; those teleutospores usually 

 have thin walls. P. Malvacearum is sometimes supposed to 

 hibernate by a perennial mycelium, but there is reason to 

 believe that in most cases infection each year proceeds from 

 over-wintered teleutospores. Most of the species which have 

 these thin-walled spores also produce some with thicker walls, 

 which act as resting spores in the ordinary way. 



Besides the two-celled teleutospores, several species of 

 Puccinia also produce similar spores with only one cell — these 

 are called mesospores. A mesospore can occasionally be found 

 in many Puccinias, even in P. Caricis (Fig. 15), 

 but in others they are abundant, e.g. in 

 P. Porri, where careful search is often required 

 before a two-celled spore can be detected. 

 Mesospores arise merely by the omission of the 

 last nuclear division ; they are exactly of the 

 same nature as the two-celled teleutospores F - ,. . 

 and germinate in the same way. By this spore of P. Car- 

 means they can be distinguished from the 

 amphispores previously mentioned, but not of course from the 

 teleutospores of Uromyces. In fact authors have described 

 some species which produce them as Uromyces, overlooking the 

 rarer two-celled spores that occur with them. See remarks 

 under Puccinia Porri and Uromyces ambiguus. 



