264 Journal of Agricultural Research vo1.xix,no.6 



but it is sufficient to say that no pathologist of note has for any length 

 of time accepted this explanation of rust dissemination, 



DORMANT MYCELIUM THEORY 



There has been more support, and probably more ground for support, 

 for the theory that the mycelium of rusts may live over in the seed or 

 seed parts of the plant in a dormant state and then infect the young 

 seedlings at the time of germination. A number of writers have sug- 

 gested this possibility, among whom W. G. Smith {24) was probably the 

 first. He says: 



If apparently healthy leaves of com are taken, and apparently healthy leaves 

 of Barberry, and these leaves are microscopically examined, fungus mycelium will 

 be commonly found inside the leaves. Neither is the mycelium confined to the 

 leaves, for it invades the seeds of both plants, and these seeds are frequently planted 

 with the mycelium in their tissues. A diseased progeny is the result. 



Zukal {26), in 1899, published observations which seemed to indicate 

 to him that rust was transmitted by mycelium in seed grain. He con- 

 cluded that rust mycelium might live over in the wheat kernels because 

 the rust appeared so early on the young seedlings. He found septate 

 mycelium at the base of the sheath, in the culms, and at the nodes in the 

 parenchyma cells just under the epidermis. He concluded that the 

 mycelium lived over in the seed and in the spring grew through the 

 scutellum into the embryo and developed with the plant. 



Pritchard (22, p. 152), in 191 1, found mycelium in the roots, in both 

 central cylinder and epidermis, in the stem, and between the leaf sheaths 

 in plants grown from rusted wheat kernels. This myceUum resembled 

 rust mycelium which he found at the base of the sori upon the germ end 

 of the kernel of wheat from which the plants were grown. He states that 

 the mycelium was abundant in the young stem, filling the intercellular 

 spaces and freely penetiating cell walls as well. More will be said later 

 in regard to Pritchard's work. 



SEED-BORNE SPORES THEORY 



Massee (20) secured evidence which seemed to indicate to him that 

 seed-borne urediniospores or urediniospores in the soil might cause 

 infection of young wheat plants. More recently Blaringhem {3) and 

 Beauverie (j) have published extensive observations which they have 

 made. They conclude that Puccinia glumarum may be transmitted by 

 urediniospores borne in the pericarp of the seed. As stated above, they 

 found uredinia in abundance in the pericarp of various grains and grasses 

 and concluded that these spores, so protected, may retain their viability 

 until the germination of the seed, when they become free from the sori 

 through the rupturing of the pericarp and may infect the young plant at 

 this time. Their conclusions, in the writer's judgment, are based upon 

 insufficient experimental evidence, and, although the theory is interesting 

 in itself, certainly it should be supported by more careful experiments. 



