THE RUSTS OF NOVA SCOTIA. FRASER. 319 



at certain points ; from this intertwined hyphal mass a number 

 of branches are given oft' perpendicular to the surface of the 

 host, and from each of these branches a urediniospore is pro- 

 duced. Sometimes paraphyses are present as in Melqmpsora 

 and Phraymidium, and in a few genera a peridium is pro- 

 duced as in Pucciniastrum and Melampsoridium. 



The urediniospores are usually produced singly on pedicels 

 which soon fall away, but sometimes in chains, as in 

 Clirysomyxa and Coleosporium. When arising in chains they 

 resemble aeciospores, but the order of development will dis- 

 tinguish, the aeciospores always being produced first. The 

 urediniospores are always unicellular, with verrucose or 

 echinulate walls. They are never smooth, and are usually 

 coloured brown. Two or more germ-pores (rarely one) are 

 present which are usually evident. As the number is often 

 definite, it sometimes forms a character of value in the 

 determination of the species. 



The urediniospores germinate readily in water, as in the 

 case of the aeciospores. When mature and under favourable 

 conditions on the host plant a germ tube is pushed out through 

 one of the germ pores, which grows very rapidly, and the 

 nucleus of the spore soon passes into it. When it reaches a 

 breathing pore the tip swells into a vesicle, the appressorium, 

 into which the protoplasm of the tube collects. A thin process 

 passed down through the pore and swells into a vesicle in the 

 respiratory cavity, the protoplasmic contents soon pass into 

 the internal vesicle. Tubes or hyphae are soon formed from 

 this vesicle which make their way among the cells. The 

 development of the haustorium begins as a minute process from 

 the hypha, which pierces the cell wall and at once swells up 

 at its distal extremity into a minute head. Soon this grows 

 out, often as an irregularly branched or variously shaped body. 

 In many cases the growth is directed toward the nucleus and 

 infection is complete. (Ward. Phil. Trans. Roy. Society, Lon- 

 don. R, 100: 20-46. 1002). 



