DIV. I 



THALLOPHYTA 



457 



differently, and recent researches show that Puccinia and other genera agree. 

 Here also the ends of the hyphae (A} divide into a terminal sterile cell and a 

 lower fertile cell (), but the 

 fertile cells fuse in pairs with 

 one another, the upper portions 



of the separating walls breaking (\< 



down ((7). The two nuclei lie 

 side by side and divide simul- 

 taneously (conjugate division). 

 Two of the daughter nuclei 

 remain in the lower part and two 

 pass to the upper portion of the 

 dividing cell, and this upper 

 portion is separated by a trans- 

 verse wall as fhe first spore- 

 mother-cell (D). In other re- 

 spects the formation of the 

 aecidiospores proceeds as de- 

 scribed above. A peridium is 

 not formed in Phragmidium, 

 but in Puccinia, etc. it arises 

 from the sterile peripheral chains 

 of spores and from the sterile terminal cells of the central rows of spores. 



The ripe, binucleate aecidiospores (Fig. 406 D) are shed and infect a new host 



FIG. 404. Gymnosporangium davariaeforme. A spermo- 

 gonium rupturing the epidermis of a leaf of Crataegus ; 

 sp, spermatia ; p, sterile paraphy ses. (After BLACKMAN. ) 



FIG. 405. Puccinia graminis. Aecidium on Berberis vulgaris ; ep. epidermis of lower surface of leaf ; 

 m, intercellular mycelium ; p, peridium ; s, chains of spores, (x 142.) 



plant. Each spore gives rise to an intercellular mycelium which soon proceeds in 

 the summer to bear UREDOSPORES or summer spores. These appear in small circular 

 or linear groups and arise singly from the enlarging terminal cells of the hyphae 



