74 THE AMERICAN MONTHLY [Mar 



only one — that the germ- tube issues. It in these germ- 

 tubes which, finding their way through the stomata of the 

 host-leaf, start densely woven mycelial growths in the in- 

 tercellular spaces of its tissue. The mycelial tubes not 

 infrequently develope tubular suckers, called haustoria, 

 which penetrate the cells themselves, abstracting their 

 manufactured food-stuffs for the benefit of the parasite. 



The mycelium present in the leaves of the- host-plant 

 {i. e. the pea) resulting from inoculation by the secidio- 

 spores, gives origin to the first crop of uredospores, which 

 are produced singly at the tips of short branches of the 

 mycelium. The epidermis is ruptured, and they appear 

 on the surface as orange-colored patches or sori. The 

 uredospores thus formed germinate on other pea leaves, 

 and produce successive crops of uredospores throughout 

 the summer ; and finally in the autumn, the same myce- 

 lium produces a crop of teleutospores, which form dark 

 brown sori on the surface of the leaf, and these, as said 

 before, rest during the winter either in the soil or on the 

 surface in connection with the decayed leaves, producing 

 in the spring the pro-mycelial spores which inoculate the 

 newly developed foliage of the spurge. 



The uredospores are spiny, of a yellowish brown, and 

 1-1250 of an inch in diameter. They are said to have as 

 many as six germ-pores, and never less than two. The 

 germination and mode of attack on the host-plant are 

 the same as in the case of the aecidiospores. 



The teleutospores, darker in color than the other 

 forms, are produced generally at their period of decay. 

 In some species this is the only form of spore known. 

 They are unicellular in U. pisi, this being the invariable 

 rule in the genus; and there is not more than one spore 

 developed at the end of each pedicel. They are 1-800 

 of an inch in their long diameter by 1-1250 of an inch in 

 their shorter one. The teleutospores of ail Puccinias 

 are bi-cellular. 



