448 



BOTANY OF THE LIVING PLANT 



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 spennogonia composed of hyphae pointing radially 

 inwards, while from the end of each a minute non-motile spermatium 

 is abstricted. These not having been found capable of causing 



infection, are held to be non-functional 

 male organs (Fig. 383, s). The bodies 

 on the lower surface are larger, and 

 develop when mature into the cup- 

 like aecidium-fruits. Each is com- 

 posed of an outer sheath, or peridium, 

 while the cup is filled with filaments 

 rising from the base, from each of 

 which a chain of aecidiwn- spores is 

 produced. The oldest are distal, and 

 they are shed in succession from the 

 downward-turned cups (Fig. 383, ce). 

 The ripe spores are hi-nucleate. De 

 Bary in 1865 showed that if sown on 

 young grass-leaves they infect them, 

 and produce the Rust again. Thus 

 there are two stages in the hfe-cycle, 

 '^'Wl ^^'•^ "^^-^Oj which differ in host and in propa- 



gative organs : the one has paired 



nuclei, and may be held as a diploid 



Fig. 384. sporophyte : it grows on the Grass. 



Phragmidiumviolaceum. A portion oi a -phc Other haS a siuglc nUClcUS in 

 young aecidium; st, stenle cell; a, fertile ° 



cells: at ao the passage of a nucleus from gach ccll, and may be held to be a 



a neighbounng cell is seen. B, formation ' -^ _ 



of the first spore-mother-cell, sm, from the haplotd mmetOphyte .' it QrOWS OU the 



basal cell (a) of one of the rows of spores. r o r ^ o 



C, a further stage, in which from snii the Burbevry. 



first aecidiosopre (a) and the intercalary cell 



(2) have arisen ; smo the second spore- Xhe question of sexuality in the Rust- 



mother-cell. D, npe aecidiospore. (After _ . "^ ^ , -^ , . 



Blackman.) (From Strasburger.) Fungi was for long an unsolved puzzle. 



There was reason to believe that the 

 spermogonia were rightly recognised as male organs producing non- 

 motile spermatia. The key lay in the early stages of the aecidium. 

 But no carpogonium was to be found there. It is now known that 

 an apogamous nuclear pairing occurs, which replaces a sexual process, and 

 initiates the diploid stage with paired nuclei. It has been traced in Phrag- 

 midium violaceum, as consisting in the passage of the nucleus of one cell into 

 a neighbouring cell, very much as has been seen in certain apogamous Ferns 

 (Fig. 384). But here the nuclei do not fuse at once : the receptive cell remains 

 bi-nucleate, and divides as such into a chain of bi-nucleate spores {a), and 



