POLYMORPHISM. 187 



stance occurs with Puccinia violarum, Link., and TricJiolasis vio- 

 larum, B.; with Puccinia fallens, C., arid Trichobasisfallcns,'DesTn.; 

 also with Puccinia menHice^ P., and TricJiolasis Laliatarum, D. C. 

 In Jlfelampsora, again, the prismatic pseudospores of Melampsora 

 salicina. Lev., are the winter fruits of Lecythea caprearum. Lev., 

 as those of Melampsora populina, Lev., are of LecytJiea populina, 

 Lev. In the species of Lecythea themselves will be found, as De 

 Bary * has shown, hyaline cysts of a larger size, which surround 

 the pseudospores in the pustules in which they are developed. 



A good illustration of dimorphism in one of the commonest of 

 moulds is given by De Bary in a paper from which we have 

 already quoted.f He writes thus : In every household there is 

 a frequent unbidden guest, which appears particularly on pre- 

 served fruits, viz., the mould which is called Aspergillus glaucus. 

 It shows itself to the naked eye as a woolly floccy crust over 

 the substance, first purely white, then gradually covered with 

 little fine glaucous, or dark green dusty heads. More minute 

 microscopical examination shows that the fungus consists of 

 richly ramified fine filaments, which are partly disseminated in 

 the substratum, and partly raised obliquely over it. They have 

 a cylindrical form with rounded ends, and are divided into long 

 outstretched members, each of which possesses the property 

 which legitimatizes it as a vesicle in the ordinary sense of the 

 word ; it contains, enclosed within a delicate structureless wall, 

 those bodies which bear the appearance of a finely granulated 

 mucous substance, which is designated by the name of proto- 

 plasm, and which either equally fills the cells, or the older the 

 cell the more it is filled with watery cavities called vacuoles. 



All parts are at first colourless. The increase in the length 

 of the "filaments takes place through the preponderating growth 

 near their points ; these continually push forward, and, at a 

 short distance from them, successive new partitions rise up, 

 but at a greater distance, the growth in the length ceases. 

 This kind of growth is called point growth. The twigs and 



* De Bary, " Uber die Brandpilze" (Berlin, 1853), pi. iv. figs. 3, 4, 5. 

 f A. de Bary, on Mildew and Fermentation, in " Quarterly German Magazine," 

 vol. ii. 1872. 



