388 CLASS BASIDIOMYCETEAE 



attached antherid in this primordium. The more recent investigations 

 seem to show that this report is incorrect. In the dense portion of the 

 pseudoparenchymatous tissue there begin to appear cells with two or 

 more nuclei, whose origin will be discussed in the succeeding paragraphs. 

 These cells elongate and may branch. At the apex binucleate aeciospores 

 are budded off. After each spore is formed there is produced a smaller 

 "disjunctor" cell, likewise binucleate, then another aeciospore, etc., until 

 a chain of alternate spores and disjunctor cells results. Between the 

 original binucleate or plurinucleate cells others push their way in from 

 the basal side of the aecial primordium and these also give rise to spore 

 chains. In the meantime the large almost empty cells begin to collapse 

 and digest, forming a space into which the chains of spores are pushed. 

 Finally all of this tissue is crushed or destroyed. Around the sporogenous 

 area a peridium may be produced or it may be wanting. The mass of 

 spores eventually ruptures the overlying host tissues and the mass of 

 spore chains and loose spores is exposed to the air. The spores are usually 

 light to dark yellow or orange and somewhat roughened. 



Craigie demonstrated in 1927 that for Puccinia graminis Pers., grow- 

 ing on barberry (^Berheris vulgaris L.) and P. helianthi Schw., growing on 

 sunflower (Helianthus) an infection with a single sporidium produces a 

 sorus within which are produced numerous spermogonia and aecial 

 primordia. If this is protected from the visits of insects the primordia 

 never develop to spore production. However, if insects are allowed free 

 access to this sorus and other sori as well, the aecia will develop within a 

 few days. Furthermore, by transferring the sperm cells from one sorus to 

 another in about half of the cases aecia will develop. Craigie finally 

 demonstrated that the four sporidia of a promycelium were of two sexual 

 phases, two sporidia of each phase, and that sperm cells from the sorus of 

 one sexual phase, would fertilize the sorus of the other sexual phase, and 

 vice versa. In later papers (1928, 1931, 1933) he has added P. coronata 

 Corda, P. pringsheimiana Klebh. (P. caricis grossulariata Arth.) and 

 Gymnosporangium sp. to the list. Miss Allen (1932a) showed this to be 

 true for P. triticina Erikss. (P. ruhigo-vera triiici (Erikss. & Henn.) Carl.) 

 and several other species of rusts. Indeed it seems probable that almost 

 all rusts producing spermogonia have these two sexual phases. If two sori 

 from sporidia of opposite sexual phases lie close together aecia will develop 

 where their myeelia come into contact, without the help of the sperm cells. 

 Brown (1932) showed that a dicaryon mycelium (e.g., uredial sorus) can 

 also induce aecial formation in a sorus from a sporidial infection. Hanna 

 (1929a) found that 48 hours after a mixture of sperm cells of opposite 

 sexual phases was applied to a sorus of Puccinia graminis Pers., on the 

 leaf of barberry, the cells at the base of the aecial primordium became 

 binucleate. Using mixtures of sperm cells from different physiologic races 



