PHYTOPHTHORA INFESTANS. 



319 



though less completely, upon fragments of leaves, which we place 

 bodily under the microscope. The gonidiophores appear as deli- 

 cate, unseptate threads, branched above, and filled with finely- 

 granular protoplasm (Fig. 115, A). The branching is monopodial 

 (or racemose) ; the number of branches usually only two or three. 

 These branches are irregularly swollen at intervals. In dry air 

 the gonidiophores, collaps- 

 ing, are twisted upon their 

 axis. Here and there we 

 see at the end of a branch a 

 gonidangium in course of 

 development ; the ripe lemon- 

 shaped gonidangia, how- 

 ever, have fallen off in laying 

 the preparation in water. In 

 order to find the gonidangia 

 on the gonidiophore, we must 

 examine the preparation dry, 

 covering it with a cover-glass, 

 and running a trace of water 

 under it from the edge, as 

 otherwise the gonidiophores, 

 as already indicated, rapidly 

 drying, shrivel up. In plants 

 collected from the open air 

 the gonidiophores are found 

 only on the under side of the 

 leaves, and do not grow so 

 tall as in the moist chamber ; 

 are much less noticeable, 

 therefore, with the naked 

 eye. 



Delicate cross - sections 

 through the margin of a spot 



FIG. 115. A, surface view of the epidermis 

 of the leaf of Solanum tuberosum (the potato), 

 with the gouidiophores of Phytophthora infest- 

 ans projecting out of the stomata (x 90) ; B, a 



3 i ripe gonidaugiuin; C, another, with divided con- 



on a diseased leaf, made by te ^ D a 8 8War 'm-gpore (B-D x 540). 



means of elder-pith, permit 

 us to clearly follow the exit of the gonidiophores from the stomata. 

 Often several such hyphae come side by side out of the same 

 stoma ; or, more commonly, the hypha branches at its exit, and 

 gives rise to gonidiophores in proportion. From these places we can, 

 though with difficulty, follow the hyphae inwards, into the tissue 



