DIV. I 



THALLOPHYTA 



459 



Barberry they germinate at once. The germ -tube penetrates the cuticle, and 

 there forms a mycelium which gives rise to spermogouia on the upper side of the 

 leaf and to aecidia on the under side (Fig. 405). On the rupture of the peridinm 

 the reddish -yellow aecidiospores are conveyed by the wind to the haulms and 

 leaves of grasses, upon which alone they can germinate. The mycelium thus 

 developed produces at first uredospores (Fig. 403, 5). They are unicellular, 

 studded with warty protuberances, and provided with four equatorially-disposed 

 germ - pores. Their protoplasm contains reddish - yellow fat globules. The 

 uredospores are capable of germinating at once on the wheat, and thus the rust 

 disease is quickly spread. Towards the end of the summer the same mycelium 

 produces the dark brown, thick-walled teleutospores (Fig. 403, 1), which in this 

 species are always double, being united in pairs. Each teleutospore is provided 

 with one germ-pore, and on germination in the succeeding year the cycle is begun 

 afresh. The mycelium of the uredo-form may hibernate in winter wheat, and 



FIG. 407. Phragmidium speciosum. A, The first rudiment of au aecidium beneath the epidermis of 

 a leaf of Rosa. B, The division of the end-cell of a hypha into the upper, transitory, sterile cell 

 and the lower fertile cell. C, Conjugation of two adjoining fertile cells. D, Later stage in which 

 the first nuclear division is completed. E, Abstriction of the first aecidiospore mother-cell. F, 

 Chain of aecidiospores (aj, Oo) separated by intercalary cells (zj, z. ; sm, the last-formed spore- 

 mother-cell still undivided. (After CHRISTMAN.) 



thus the rust may appear in the spring without the previous formation of 

 basidiospores or of aecidia ( 80 ). 



All Uredineae do not exhibit so complicated a course of development as Puccinia 

 graminis. Rust fungi which produce all the forms of spore are termed eu-forms ; 

 those without uredospores, opsis- forms; those without aecidia, brachy - forms ; 

 those without aecidia and uredospores, micro-forms. In those Uredineae which 

 no longer possess aecidia and spermogonia, the cells of the vegetative mycelium 

 arising from the basidiospore are uninucleate, but subsequently, before the 

 formation of the teleutospores, binucleate cells are found. The binucleate 

 condition is attained, as has already been shown for several species, in the 

 preparation for the development of the first uredospores or, when these are 

 wanting, for the first teleutospores (e.g. in Puccinia Malvacearum). It results 

 from the conjugation of two cells, as has already been described for the developing 

 aecidium. This supports the homology of the three kinds of spore. 



The genus Endophyllum ( 81 ), the species of which are parasitic on Sempervivum 



