438 



BOTANY OF THE LIVING PLANT 



A section through an infected spot on the Barberry leaf shows the 

 effect of the attack in the greatly increased thickness as compared 

 with the normal leaf (Fig. 337)- The enlarged cells of the mesophyll 

 appear enveloped by fungal hyphae which choke the intercellular 

 spaces. They are massed chiefly at points towards the upper and 

 lower surfaces, to form bodies of considerable size. The first are 

 the flask-shaped spermogonia com- 

 posed of hyphae pointing radially 

 inwards, while from the end of each 

 a minute non-motile spermatium is 

 abstricted. These have not them- 

 selves been found capable of causing 

 infection ; but they may stimulate 

 development and are possibly male 

 organs {sp). The spermogonia secrete 

 a fluid, sometimes described as " nec- 

 tar " in which large numbers of 

 spermatia may be present. Projecting 

 beyond the spermogonial opening or 

 ostiole are long flexiwus hyphae. The 

 bodies on the lower surface are larger 

 and develop into the cup-like aecid- 

 ium-fruits. Each is composed of an 

 outer sheath or peridium, while the 

 cup is filled with filaments rising from 

 the base, from each of which a chain 

 of aecidiospores is produced. The 

 oldest are distal, and they are shed 

 succession from the downward- 



m 



Fig. 338. 



Phragmidium violaceum. A, portion of a 

 young aecidium ; st, sterile cell ; a, fertile 

 cells : at a 2 the passage of a nucleus from 

 a neighbouring cell is seen. B, formation 

 of the first mother-cell, sm, from the basal 



turned cups (Fig. 337,*). When ripe ^ $ & \£S££>^ *jSinT 

 they are bi-nucleate. De Bary in 1865 cala !7 cell n (z) have arisen ;jm 2 the second 



J j ~> mother-cell. D, ripe aecidiospore ; note 



Showed that if SOWn On young grass- the paired nuclei. (After Blackman.) (From 



J ° ° Strasburger.) 



leaves they infect them, and produce 



the Rust again. Thus there are two stages in the life-cycle, which 

 differ in host and in propagative organs : the one has paired nuclei, 

 and may be held as a diploid sporophyte : it grows on the Grass. The 

 other has a single nucleus in each cell, and may be held to be a haploid 

 gametophyte : it grows on the Barberry. 



The problem of sexuality in the Rusts is still not entirely solved. In some 

 species, cluster-cups develop after infection by a single sporidium ; in others 

 mycelia from two sporidia must meet, or a mycelium must be stimulated by 



