CRYPTOGAMS 



405 



lecidium is formed of thick-walled cells corresponding 'to the sterilised peripheral 



rows of spores. In Phragmidiiim violaceum, which occurs on Blackberry leaves 



and has been fully investigated 



by BLACKMAN ( 76 ), the hyphen 



beneath the epidermis when 



about to give rise to an secidiuni 



iir.st cut off a sterile cell, which 



undergoes no further develop- 



ment, from their ends (Fig. 351 



A}. The cell below this increases 



in size ; it has at first only a 



single nucleus but becomes bi- 



nucleate by the passage of a 



nucleus into it from an adjoining 



mycelial cell. The two nuclei do 



not fuse. The bimicleate cell 



undergoes successive divisions 



into achainof spore-mother-cells, 



each of which has a pair of nuclei; 



FIG. 349. Gymnoxporungium davariacforme. 



goniuni rupturing the epidermis of a leaf of Crataegus ; 

 sp, spennatia ; p, sterile paraphyses. (After BLACKMAN.) 



and from each spore-mdther-cell 



an upper binucleate aecidiospore 



and a sterile intercalary cell, 



which is also binucleate but soon shrivels up, are derived by a transverse 



division (B, O). 



Fio. 350. I'uccinia graminis. /Ecidium on Herberts vulgaris ; </, epidermis of lower surface of leaf ; 

 I'm, intercellularlmycelium yep, peridiumi; , chains of spores. (x!142.) 



According! to ^CHRISTMAN ( 76 ) the development of the secidiospores in Phrag- 

 midium spetiosum (Fig. 352), which is parasitic on Rosa, proceeds somewhat 

 differently. Here also the ends of the hyphse (A) divide into a terminal sterile cell 



