ORDER UREDINALES (tHE RUSTS) 



385 



a tertiary or even quaternary sporidiiim, each being shot off from its 

 sterigma. The successive sporidia are smaller and smaller. Under condi- 

 tions of extreme humidity the author has observed the primary sporidia 

 and the succeeding ones of Kunkelia nitens (Schw.) Arthur remaining 

 attached in a short chain of four or five successively smaller cells. 



When a sporidium falls upon the epidermis of a suitable host it germi- 

 nates in a drop of rain or dew or film of water, forming a slender germ tube 

 which, Dr. Ruth F. Allen (1930) showed, penetrates the cuticle and cell 

 wall into the epidermal cell. The actual pore of entry is very small, the 

 hypha on either side being several times as thick. Within the epidermal 

 cell the hypha elongates and becomes 

 divided into several uninucleate cells. 

 From each of these a branch grows 

 through the interior wall of the host 

 cell either into an underlying cell, 

 where it acts just as did the infection 

 hypha in the epidermal cell, or into 

 an intercellular space where growth 

 becomes much more rapid and the 

 hypha becomes larger and more vigor- 

 ous, sending haustoria into the cells 

 between which it passes. A few cases 

 have been reported where entry took 

 place through a stoma but these seem 

 to be not usual. Pady (1935) reports 

 that in the uninucleate race of Kun- 

 kelia nitens the sporidia upon germi- 

 nation infect intracellularly the epi- 

 dermal cells and from these continue 



to progress as intracellular mycelium for ten days or so, producing then 

 in the phloem tissues of the host the intercellular mycelium which forms 

 haustoria that are coiled more or less. More often after the first two or 

 three cells are formed the production of septa leads to the formation of 

 uninucleate (monocaryon) cells. In Melanipsora lint (Pers). Lev. the cells 

 remain one to three or four nucleate up to the regions where the definite 

 reproductive cells are formed when monocaryon cells predominate (Allen, 

 1934a). The infected area of the leaf often becomes thickened, in part at 

 least through rapid formation of large amounts of mycelium which forces 

 the host cells apart and in some cases crushes them. The presence of the 

 rust may cause marked changes in the manner of growth of the host. In 

 normally prostrate species of Chamaesyce {Euphorbia) the infected shoots 

 become upright, a phenomenon also observed in other families of host 

 plants. Abnormal growth of axillary buds in infected shoots gives rise to 



Fig. 127. Subclass Teliosporeae, 

 Order Uredinales. Infection of leaf of 

 Berberis vulgaris L. by sporidium of 

 Puccinia graminis Pers. Infection 

 hyphae are within epidermal cell and 

 the attached sporidium is empty. 

 (Courtesy, Allen: J. Agr. Research, 

 40(7):585-614.) 



