308 



PTJCCINIA. 



443. Structure of Aecidium. Examine carefully with high 

 power a young 1 aecidiuxn, which has not yet burst through the 

 epidermis, and compare its structure with that of the mature 

 aecidiuxn.. 



In the mature aecidium note (1) the dense hyphae at the base of 

 the aecidium; (2) the layer of closely packed parallel rod-like 

 hyphae above this ; (3) the row of aecidiospores produced in 

 basipetal sequence by abstriction from each of these rod-like hyphae ; 



(4) in each row the orange-coloured thick-walled spores, of polygonal 

 (hexagonal in section) form owing to the close packing of the rows ; 



(5) the presence of small much flattened interstitial cells alter- 

 nating with the spores in each row ; (6) the outer wall of the aeci- 

 dium, consisting of a layer of cells with very thick cell-walls (the 

 outer wall especially thick and striated) this layer evidently corre- 

 sponds to sterilised rows of aecidiospores. 



Mount in water some loose aecidiospores, and note the (usually 

 six) thin places or pits ("germ-pores ") in the cell- wall. 



444. Structure of Spermogonium. In a spermogonium, 



with the high power, note (1) in the lower portion the closely packed 

 parallel rod-like hyphae or sterigmata, converging to the centre of 

 the flask-like cavity ; (2) the upper hyphae or paraphyses project- 

 ing in a tuft from the raised apical pore ; (3) the numerous small 

 ovoid cells or spermatia abstricted from the sterigmata. 



445. Culture of Aecidiospores and Spermatia. Remove 

 some aecidiospores from a ripe aecidium, place them in a drop of 

 water on a Wheat seedling, keep moist by placing it on wet blot- 

 ting-paper under a bell-glass. After two or three days, cut tangen- 

 tial sections of the epidermis, and look for germinating spores, 

 putting out a hypha which enters the leaf through a stoma. If this 

 is not seen in a few days, try another lot, since germination nor- 

 mally occurs within two or three days. 



Tease spermatia from a spermogonium, and grow them in a hang- 

 ing drop of Pasteur's solution or a weak sugar solution ; they may 

 germinate, put out hyphae, and buds like Yeast cells, but they do 

 not continue to grow for long, nor are they capable of infecting 

 either host (Barberry or Wheat). 



446. Aecidia, etc., of other Uredineae. The aecidium stage 

 on the Barberry is not essential for the vigorous development of 

 Wheat Rust, and is in fact very rarely found. Where Barberry 

 bushes are rare or absent in a district, use the aecidia of other 

 Uredineae. These may be found, especially in spring and early 

 summer, on Buttercups, Lesser Celandine, Violet, Coltsfoot, Sting- 

 ing Nettle, Docks, etc. 



Also examine the uredospores and teleutospores of the Rusts which 

 attack such plants as Mallow, Hollyhock, Chrysanthemum, etc. 



