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 spermogonia 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 aecidium-spores is 

 produced. The oldest are distal, and 

 they are shed in succession from the 

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

 The ripe spores are bi-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 life-cycle, 

 which differ in host and in propa- 

 gative 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 



FIG. 384. 



Phragmidium violaceum. A , portion of a 

 young aecidium; st, sterile cell; a, fertile 

 cells : at 0-2 the passage of a nucleus from 

 a neighbouring cell is seen. B, formation 

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

 basal cell (a) of one of the rows of spores. 

 C, a further stage, in which from smi the Barberry. 



first aecidiosopre (a) and the intercalary cell 

 (*) have arisen ; sm? the second spore- 

 mother-cell. D, ripe aecidiospore. (After 

 Blackman.) (From Strasburger.) 



The question of sexuality in the Rust- 

 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 



