STRUCTURE. 37 



cellular passages, and may sometimes be found in parts of the 

 plants where the fungus does not develop itself. There is no 

 proper excipulum or peridium, and the spores spring direct 

 from a more compacted portion of the mycelium, or from a 

 cushion-like stroma of small cells. In 

 Lecythea,i\ie> sub-globose spores are t.fc 

 first generated at the tips of short 

 pedicels, from which they are ulti- 

 mately separated ; surrounding these 

 spores arise a series of barren cells, 

 or cysts, which are considerably larger FIG. i6.-Barren cysts andPseudo- 

 than the true spores, and colourless, 



while the spores are of some shade of yellow or orange.* In 

 Trichobasis, the spores are of a similar character, sub-globose, 

 and at first pedicellate ; but there are no surrounding cysts, and 

 the colour is more usually brown, al- 

 though sometimes yellow. In Uredo, 

 the spores are at first generated singly, 

 within a mother cell ; they are globose, 

 and either yellow or brown, without 

 any pedicel. In Coleosporium, there 

 are two kinds of spores, those of a 

 pulverulent nature, globose, which are 

 sometimes produced alone at the com- 

 mencement of the season, and others FIG. 17. Coleosporium 

 which originate as an elongated cell ; 



this becomes septate, and ultimately separates at the joints. 

 During the greater part of the year, both kinds of spores are to 

 be found in the same pustule. In 

 Melampsora, the winter spores are 

 elongated and wedge-shaped, com- 

 pacted together closely, and are only 

 matured during winter on dead leaves : 



FIG. 18. Melampsora salicina. 



the summer spores are pulverulent 



and globose, being, in fact, what were until recently regarded 



* Le"veille, " Sur la Disposition Me"thodique des Ure'dine'es," in "Ann. des 

 Sci. Nat." (1847), vol. viii. p. 369. 

 3 



