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110TAL nORTICULTTJBAL SOCIETY. 



rusts and mildews of cereals and other plants which are known to 

 botanists under the names of Uredo, Paccinia, JEcidium, and a 

 host of allied genera ; but we have now, in addition, reason to be- 

 lieve that the same species may, at different periods of growth, 

 require a different matrix, after the fashion of many parasitic 

 Invertebrata. 



It is not possible to give the whole of De Bary's introductory 

 observations. The following seem, however, necessary to the 

 proper appreciation of his argument. 



Some of the allied parasites which have been the subject of his 

 experiments, as Uromyces appendiculatus, Lk., V. pliaseolorum, 

 Tub, and Puccinia Tragopogonis, Cd., possess five kinds of repro- 

 ductive organs. Towards the end of the year shortly stipitate 

 spores appear on their stroma, which do not fall off. These spores, 

 which do not germinate till after a shorter or longer winter rest, 

 may conveniently be called resting-spores, or, as De Bary calls 

 them, teleiitospores, being the last which are produced. These at 

 length germinate, become articulated, and produce ovate or kidney- 

 shaped spcres, which in their turn germinate, penetrating the 

 cuticle of the mother-plant, avoiding the stomates or apertures by 

 which it breathes. After about two or three weeks the mycelium, 

 which has ramified among the tissues, produces SLiisEcidium with its 

 constant companion spermagonia, — distinct cysts, that is, from 

 which a quantity of minute bodies ooze out, often in the form of 

 a tendril, the function of which is imperfectly known at present, 

 but which, from analogy, we regard as a form of fruit, though it is 

 just possible that they may be rather of the nature of spermato- 

 zoids. The 2Ecidia contain within a cellular membranous sac a 

 fructifying disk which produces necklaces of spores, which ulti- 

 mately separate from each other in the form of a granular powder. 

 The grains of which it is composed germinate in their turn, no 

 longer avoiding the stomates as before, but penetrating through 

 their aperture into the parenchym. The new resultant mycelium, 

 reproduces the Uredo or fifth form of fructification, and the Uredo- 

 spores fall off like those of the JEcidium, and in respect of germi- 

 nation and mode of penetration present precisely the same 

 phenomena. The disk which has produced the ZTmfo-spores now 

 gives rise to the resting-spores, and so the cycle is complete. 



AVe are not, however, to expect in every case precisely the same 

 cycle, though it seems not to be an uncommon one, and in the 

 case before us, the whole evolution has not been carried out. In 

 some cases certainly there is no intermediate ^Ecidium, and in 



