Uredospores. 19 



CHAPTER VI. 



UREDOSPORES. 



Uredospores may originate from the hyphae developed from the germ- 

 tube of an aecidiospore, a promycelial spore, or another uredospore. They 

 are generally ovate or elliptic, and are developed singly on the ends 

 of separate short upright hyphae, known as basidia. In some 

 genera, however, such as Coleosporium and Chrysomyxa, they arise like 

 the aecidiospores, in short chains, and thus resemble Caeoma- forms in 

 fact, they are sometimes regarded as such. The spore-bearing hyphae are 

 crowded together just beneath the cuticle, or epidermis, of the plant, and 

 such an aggregation is known as a spore-bed, or sorus. 



The uredospores are always unicellular, and never smooth, the mem- 

 brane being beset with projections in the form of short prickles (echinulate) 

 or fine warts (verrucose). Two-celled uredospores have ibeen described and 

 drawn by Roze l and Jacky 2 , in Puccinia chrysanthemi, but they are 

 very probably monstrosities, as suggested by Sydow, two unicellular spores 

 becoming united when young, and growing up together. In the same rust 

 I found, in one instance, two uredospores produced on the same stalk, the 

 one slightly beneath the other ; but this was merely a freak. They differ 

 generally from the aecidiospores on the one hand in the mode of forma- 

 tion, and from the unicellular teleutospores of the genus Uromvces on the 

 other, in having two or more germ-pores, and this character also dis- 

 tinguishes them from the .mesospores. Only in exceptional cases is there 

 only one, as in Puccinia monopora. They vary in colour, generally being 

 some shade of orange or brown, and in the brown spores De Bary has 

 shown that, as in teleutospores generally, the colouring matter is in the 

 wall, and not in the contents. 



Germination occurs similarly to that of the aecidiospores. When ripe, 

 and kept moist, a germ-tube is readily protruded through one or more 

 of the germ-pores, and this enters the host-plant by a stoma, and' in 

 the interior develops a mycelium like that from which it originated. 



It is interesting to notice that in some cases the uredospores may be 

 produced, not only at the surface, but within the tissues. This happened 

 with Puccinia pruni, in a peach fruit, where spore-beds of rust freely 

 producing uredospores were imbedded in the tissue, in more or less 

 roundied cavities, up to 5 mm. below the surface. The decaying fruit would 

 form a splendid matrix for preserving the spores till next season. Since 

 they are chiefly produced in the summer, and adapted, as a rule, for 

 rapid germination, they are often spoken of as summer spores, and as 

 soon as they arrive at maturity become detached from their stalks. 



Repeated Formation of Uredospares. Just as aecidiospores may -pro- 

 duce aecidiospores for several generations, so may uredospores produce 

 uredospores. This is well seen, for instance, in P. graminis. where uredo- 

 spores are produced direct from the uredospores without the intervention 

 of aecidia and teleutospores, as is the case in Australia, and this repeated 

 formation of uredospores may continue indefinitely. But there are several 

 cases where the first-formed uredospores are different from those produced 

 later, and, in order to distinguish such forms, the two kinds of generations 

 are known respectively as primary and secondary 



