542 



RESEARCHES ON FUNGI 



their exterior, the uredospores being echinulate or verrucose and 

 the aecidiospores verrucose (Fig. 218, a and c). In contrast with 

 the uredospores and aecidiospores, the teleutospores, with few 

 exceptions, are smooth (Figs. 218, d, and 222, b, p. 546). This 

 structural difference is correlated with a difference in function. 

 The uredospores and aecidiospores act as organs of dissemination 

 and, as such, are freely liberated and blown about as powder by 

 the wind. Their rough exterior probably assists them in attaching 

 themselves to the surface of their host-plants when they have once 



settled upon them. On the other hand, teleuto- 

 spores, as a rule, are not organs of dissemina- 

 tion but probasidia destined merely to produce 

 basidia upon which organs of dissemination 

 (basidiospores) may arise. They are therefore 

 anchored to their hosts, usually by stout 

 pedicels, and are not set free. An echinulate 

 surface would be of no use to them and is there- 

 fore not developed. 



As already indicated, there are a few Rust 



fungi which, in contrast with the vast majority, 



densely^covered with posscss teleutospores which are not smooth but 



large warts. From j^^^g sculptured walls. Several of these fungi, 



W.B. Grove sBri<?s/i ^ _ ° 



e.g. Polythelis Pulsatillae, P. Thalictri, and 

 P. fusca, have pycnospores and teleutospores 

 only, while the teleutospores are remarkable in being pulverulent 

 (Fig. 219).^ It appears therefore that, in the absence of uredospores 

 and aecidiospores in these species, the teleutospores, while still retain- 

 ing their probasidial function, have become detachable and thus 

 converted into organs of dissemination. It seems probable that the 

 walls of the teleutospores became sculptured as the teleutospore- 

 sorus became pulverulent and some advantage could be gained by 

 the teleutospores attaching themselves after transportation through 

 the air, to their host-plants or other substrata upon which they 

 happened to fall. 



^ J. C. Arthur, North American Flora, The Uredineae, vol. vii, part ii, 1907, 

 pp. 152-153. Polythelis is one of the sub-divisions of the old genus Puccinia. 

 Arthur states, for all three of the species I have mentioned, that the two cells of the 

 teleutospore easily separate. 



Fig. 219. — Puccinia 

 fusca. Two teleuto- 

 spores, very much 

 constricted, com- 

 posed of two almost 

 globose or oblong 

 cells which easily 



Rust Fungi. Magni- 

 fication, 600. 



