326 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



mycelium creeps through the bark so as to make its appear- 

 ance again in a new spot at some distance from the original 

 position ; as Dr. Brown suspects may be the case with some 

 of those parasitic plants which appear from the bark at once, 

 under the guise of large flowers, without any save rudimentary 

 foliage. In neither case, however, is the position perfectly 

 demonstrable, though highly probable. TriiDhragmium is 

 distinguished from Puccinia by the addition of a vertical 

 septum as well as the horizontal one. In Aregma the cells are 

 greatly multiplied, and the stem is curiously swollen at the 

 base ; while in Xenodochus the prothallus is extended so much 

 as to have the aj)pearance of a Torula, and thus to depart 

 from the typical character. The germination of this latter 

 genus has not been observed ; but it will, in all probability, 

 prove similar to that of its allies. 



351. Puccinia graminis has long been known as the cause 

 of mildew in wheat, a plague for which no remedy has hitherto 

 been found. Since the discovery that the bodies which 

 were supposed by Sir J. Banks to be capsules, are merely 

 anticipations of the true spores, and that germination does not 

 take place as soon as the prothallus is ripe, it is probable that 

 the remedy suggested some years since by Mr. Tycho Wing, 

 the eminent land-agent of the Bedford Level Estates, viz., 

 to allow no reeds or loose grass to remain in the ditches, but 

 to clear everything away, and to consume it at once, is one 

 of the most effectual. As the species which attacks reeds and 

 grass is to all appearance the same with that of the wheat, 

 the disease may be propagated in the spring from such out- 

 liers. For the same reason, it is desirable that the stubble 

 should not be left on the land too long, and, indeed, long 

 mowing must be better than reaping. With the exception of 

 a few Puccinice, the Fungi of this group are natives of tem- 

 perate regions. Aregma is rare in America, but there is one 

 most beautiful species which may vie with any of ours (Fig. 

 73, a), as may the Podisoma macropus with our native 

 species. Acalyptospora, Desm., is perfectly free, but I am 

 not certain of the affinities of the genus, nor, indeed, whether 

 it is a true Fungus. 



