PYCNIA OR SPERMOGONIA 311 



attackino- Rosaceae and Ranunculaceae have acervular or hemi- 

 spherical pvcnia. 



All pvcnia consist of a palisade of slender sporophores that 

 arise from a pseudoparenchymatous tissue. Toward the upper 

 part or the periphery sterile sporophores or paraphvses form a 

 column that extends beyond the surface of the host. In species 

 of Alilesia, however, paraphyses are wanting. Spherical to oval 

 spores (spermatia) are abstricted in series from the apices of the 

 sporophores. The mass of spermatia accumulates to the extent 

 of rupturing the overlving host tissues or of effecting an ostiole, 

 through which the spermatia ooze. The ooze is sugary and 

 sometimes gives off a fragrant odor. \^arious insects are in con- 

 sequence attracted to the exudate and serve as vectors in the dis- 

 persion of the spermatia. 



The spermatia are uninucleate, the nucleus being proportion- 

 ally large. They may germinate by forming a germ tube or by 

 budding, as was observed by Cornu as long ago as 1876. 



Opinions concerning the function of spermatia have been in 

 conflict since 1833, when Unger placed all rust spermogonia 

 under one genus and species, Aecidiohnn exanthematimi. In 1841 

 Meven regarded them as male structures but maintained that 

 there is no sexuality among rusts. Later, as the result of cyto- 

 lo^ical studies involving the formation of aeciospore mother cells, 

 a subject given more attention at another point in the discussion, 

 the opinion became established that spermogonia are vestigial 

 and non-functional. In 1927, however, Craigie (1927) observed 

 that spermogonia and aecial primordia develop from infection 

 by a single basidiospore, but that aeciospores never develop in 

 such primordia unless spermatia from one lesion are transferred 

 from one sorus to another. In these studies Craigie employed 

 Fiiccinia grmnims on barberry and P. helianthi on sunflower. 

 Later (1931) he demonstrated that the 4 basidiospores arising 

 from any basidium of these rusts are of 2 sexual phases, and that 

 the spermatia arising from 1 phase w^ill fertilize the sorus of the 

 opposite sexual phase, and vice versa. He noticed a similar situa- 

 tion in Fiiccinia coronata, P. pringsheimiana, and a species of 

 Gymnosporangium; therefore in some rusts, presumably all which 

 form spermogonia, the spermatia are functional. 



Attention has also been called by several workers [Andrus 

 (1931), Pierson (1933)] to the presence of receptive hyphae 



