DICIfOCARPISM 71 



venience, these are scarcely to be considered as diehocarpous. 

 The definition would be that each generation or form completes 

 its career in the same form as it commenced, so that each starts 

 from a germ, and the cycle is not the career of a single in- 

 dividual, but of a series of individuals which revert to the 

 original fonu after one, two, or more intermediate and different 

 generations. This phenomenon is certainly not common in 

 Fungi, but it is illustrated in the Uredines, where the series 

 consists not only of two but of several generations which inter- 

 vene between those of a like denomination. We will take a 

 supposititious example, admitting the facts for the sake of illus- 

 tration. The leaves of pear trees are not uncommonly visited 

 by a Fungus called RacstcUa cancellata, in which a cluster of 

 peridia appear on a yellow spot. When mature these peridia 

 discharge a profusion of subglobose warted brown spores. 

 This ends the first generation by the production of spores. 

 According to some these spores are drifted from the pear leaves 

 to a juniper bush, where they germinate and invest the 

 bush, producing, as a result, what is assumed to be the same 

 Fungus, in a different form, upon a new host. In this case 

 gelatinous cylindrical masses burst through the bark without 

 any peridium, consisting of elongated, two -celled, hyaline 

 spores on long pedicels, all agglutinated together by the 

 gelatine. This is the second generation, different from the 

 first, but ending in the production of spores, called specially 

 teleutospores. In the next stage these teleutospores germinate, 

 and the germ tube produces as buds small promycelial spores, 

 which are carried by the wind or otherwise back to the leaves 

 of a pear tree, producing thereon either directly or indirectly 

 the peridia of RacstcUa cancellata, and so the reversion is made 

 to the original form, after the intervention of an intermediate 

 generation as Gymnosporangium sabiiuic. Thus, then, RacstcUa 

 canccUatcL on pear leaves produces subglobose brown spores, 

 and these germinating produce Gymnosporangium sahinac, with 

 hyaline luiiseptate teleutospores on the savin, which is the 

 second generation. The teleutospores of the Gymnosporangium, 

 through the intervention of promycelial spores, reappear on 

 pear leaves as a RacstcUa, and thus the first form of fruit is 

 reached again after the intervention of a different generation. 



