ox THE WHITE RUST OF CABBAGES. 119 



between the true cuticle and the cuticular cells. To ascertain 

 this point requires rather delicate manipulation, but the fact is 

 very clear in an extremely thin slice, provided the flaccid mem- 

 brane has not unfortunately been turned aside by the edge of the 

 lancet with which the section is made. The cuticular cells, 

 however, are much confused and deranged by the growth of the 

 parasite, which is developed principally at their expense, those 

 of the succeeding layer being very little if at all affected. The 

 mycelium is closely incorporated with the cuticular cells, and 

 appears simply grumous, without distinct structure : this, how- 

 ever, may be owing to its being so delicate as to be broken up 

 under the knife ; at any rate it does not appear to be filamentous. 

 From the top of this mass, on the level of the tips of the cells, 

 on which it grows, arise very short delicate sporophores, each of 

 which is surmounted by an oblong, cylindric, often curved spore, 

 three to five times as long as broad, and containing at maturity 

 from two to tliree globose nuclei. It is highly probable that 

 each sporophore produces in succession several spores, which 

 are thus pushed forward, and in time fill the space between the 

 true cuticle and the cuticular cells, thrusting the former out 

 until it bursts. Partly owing to the successive development of 

 the spores, which are mixed with a viscid fluid, and partly to the 

 contraction of the leaf itself upon the pulpy mass, in dry weather 

 or when exposed to the direct rays of the sun, the spores ooze 

 out, kept in connection with each other by means of their attendant 

 mucilage, and drying as they are exposed to the air, form rude 

 irregular short tendrils. These tendrils are in their turn softened 

 again by moisture, and after a time fall down, forming a little 

 pellicle upon the leaf, the edges of which are often curved up 

 like a little boat or canoe, as observed originally by Dr. Gre- 

 ville. There is not the sliglitest trace of a perithecimn, so that 

 we have here one of the lowest possible forms of the group to 

 which it belongs. The spores, it should be observed, are not 

 truly truncate, as they appeared to Greville when examined by 

 the old imperfect compound microscope, but rounded and obtuse. 

 They do not arise from the division of a thread in the direction 

 of the septa, in which case they might indeed be truly truncate, 

 but from the development and expansion of a distinct cell pro- 

 duced at the tips of the sporophores. 



The question now arises to what genus is the production to be 

 assigned ? Dr. Greville was undoubtedly correct in forming a 

 new genus for its reception, for it could not be referred to any 

 established at the time in which he wrote. As said above, the 

 genus was misunderstood by succeeding observers, and the name 

 applied to very different objects. A species on ivy, clearly con- 

 generic, was published by De Notaris, in his ' Micromycetes,' 

 under the name of Myxosporium paradoxum, the specific term 



