26 Mesospores and Amphispores. 



being strongly papillate instead of echinulate, -thick instead of thin-walled, 

 with persistent pedicel and only germinating after a period of rest. Its 

 essential difference from the teleutospore is its unicellular character and 

 the possession of more than one germ-pore. 



Besides the amphispores, mesospores are very numerous in this species, 

 so that there is a Puccinia provided with two kinds of uredospores, and two 

 sorts of teleutospores. 



Up till recently this was the only instance known of the occurrence of 

 amphispores, but Arthur 5 has given descriptions and illustrations of 

 nine different species, one of which belongs to the Uromyces, in which this 

 form of spore is met with. According to this author, amphispores are 

 mainly developed in arid or semi-arid regions, and represent a resting or 

 winter form of uredospores, being provided with thickened walls to enable 

 them to withstand unfavorable conditions, just like a teleutospore. 



MESOSPORES. 



In examining the relatively large number of Australian species of Puc- 

 cinia possessing mesospores, one finds that as a rule they are comparatively 

 scarce in point of numbers, and that while a few may resemble the ordinary 

 teleutospore in colouration the majority are paler and altogether with an 

 immature appearance. But there are a few cases, such as Puccinia hetero- 

 spc-ra and P.- simplex, in which the one-celled spores far outnumber the 

 regular teleutospores, so much so that the latter have been frequently over- 

 looked, and there is every probability that they undergo germination, and 

 are therefore unicellular teleutospores in the fullest sense of the term. In 

 P. heterospora there are no uredospores, and the unicellular spores are 

 smooth, and otherwise resemble the teleutospores, while in P. simplex the 

 uredospores are spinulose and yellow, and quite distinct from the smooth 

 unicellular spores associated with the teleutospores. Owing to the teleuto- 

 spores not having been obtained at first, the former has .been variously 

 named Uromyces pulcherrimus, B. and C., U. thwaitesii, B. and Br., and 

 U. malvaceantm, Speg., and the latter as Uromyces hordei, Rost. In fact, 

 these spores have been regarded as a transition stage from the unicellular 

 Uromyces to the bicelTular Puccinia spore. In such cases the one-celled 

 spore functions as a teleutospore, and ithere would be a certain convenience 

 in distinguishing between the undeveloped and immature spores and those 

 which are fully formed, and in all probability capable of germination, 

 reserving the term mesospore for the one, and unicellular teleutospore for 

 the other. But it is so difficult to draw the line sometimes, and since it is 

 not desirable to multiply names unnecessarily, I will use the term meso- 

 spore to designate a unicellular teleutospore form in Puccinia and Uromy- 

 cladium, which may either be imperfectly developed and incapable of ger- 

 nrnation, or fully formed and germinable. 



The presence of mesospores in a species would seem to indicate its still 

 close relationship to Uromyces, and that its separation from the parent form 

 had not yet proceeded sufficiently far to obliterate every trace of its former 

 connexion. 



