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, eg. 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 yi, 15 4 meso- 
and germinate in the same way. By this spore of P. Car- 
means they can be distinguished from the  “” ae 
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. 
