DE BART ON MILDEW. 



109 



many, apparently, the JEcidium is produced on the same matrix 

 as the perfect parasite. 



Puccinia graminis, then, or true wheat-mildew, produces two 

 different kinds of spores from the same disk. Of these the first, 

 whose connexion with Puccinia was first pointed out by Professor 

 Henslow, are orange-coloured, unicellular, and echinulate, and are 

 capable of germination as soon as they are mature, but become 

 effete after a few weeks. Their germinating-threads enter the 

 stomates of the leaves and produce in a few days fresh disks, 

 covered with spores of the same kind. 



The other spores, produced at a later period, which are septate, 

 do not vegetate till they have had a longer or shorter winter's rest. 

 The germinating-threads of the secondary spores, which are pro- 

 duced on their promycelium, will not, however, penetrate the epi- 

 dermis of the mother-plant which gave rise to the resting-spores. 

 "When sown on Triticum repens, T. vulgare, and A vena sativa they 

 behaved themselves exactly as if they had been sown on glass. It 

 became probable therefore that they required some other plant as 

 a matrix for their growth, and that they produced on this an 

 uEcidiiwi after the analogy of some other species. This supposi- 

 tion was corroborated by the fact that JEcidia occur on many 

 plants which resemble in every respect those which belong to the 

 cycle of development of Puccinia, except that they are not accom- 

 panied by the two kinds of spores mentioned above, or that Puc- 

 cinoid-spores do not occur on the same mother-plant with the 

 uEcidium. These conditions concur in JEcidium JBerberidis, Grmel., 

 and the prevalent notions of its connexion with wheat-mildew 

 suggested the necessity of experiments. 



Our author determined therefore to sow the spores of Puccinia 

 graminis on the leaves of the barberry. For this purpose he 

 selected the septate resting-spores from Poa pratensis and Triti- 

 cum repens. Having caused the spores to germinate in a moist 

 atmosphere, he placed fragments of the leaves on which they had 

 developed their secondary spores on young but full-grown bar- 

 berry-leaves under the same atmospheric conditions. In from 

 twenty-four to forty-eight hours a quantity of the germinating- 

 threads had bored through the walls, and penetrated amongst the 

 subjacent cells. This took place both on the upper and under 

 surface of the leaves. Since in former experiments it appeared 

 that the spores would penetrate only in those case3 where the 

 plant was adapted to develope the parasite, the connexion between 

 P. graminis and JE. Berberidis seemed more than ever probable. 



