Spore-for))jaiion. 17 



immature spores are towards the circumference, while the older and fully- 

 formed are towards the centre. The sori generally surround the central core 

 of plant tissue as in Cintractia, but the mode of formation of the spores is 

 diiferent. The sori, to begin with, are probably distended cells, and several 

 of them run together so as to form a comparatively large cavity. In this war 

 swelling and distortion occurs, somewhat similar to that of the Club-root of 

 Cauliflower (Plate XXXIII.). 



Cintractia. 



A new genus was constituted by Cornu in 1883 on account of the develop- 

 ment of the spores in a regular manner, radiating from a central columella of 

 plant tissues and protected at first by a membrane composed of fungus cells. 

 It was named in honour of a French botanist called Cintract. This genus is 

 not universally adopted, as it is considered that the distinction between it 

 and Ustilaqo is not sufficiently marked to justify its being retained, but the 

 mode of development of the spores seems to be worthy of generic distinc- 

 tion. The mode of spore-formation has been described by Cornu l and Magnus^ . 

 The inner tissues of the host-plant form a central columella which is pene- 

 trated by the mycelium of the fungus, and this is aggregated into a compact, 

 continuous, gelatinous mass surrounding the axis. The entire outer surface 

 of this mass or stroma as it is called, may be fertile, producing spore-bearing 

 filaments, or there may be sterile rays projecting at frequent intervals be- 

 tween the spore-bearing filaments. The spores are developed in the hvphae as 

 minute colourless portions of protoplasm surrounded by a gelatinous enve- 

 lope. They are formed in succession, the oldest being always towards the 

 outside and the youngest nearest the centre. 



As they approach maturity, the gelatinous envelope is gradually absorbed, 

 the gelatinous walls of the hyphae disappear, the outer coat of the spore 

 deepens in colour, and ultimately they are quite distinct. 



In some cases the fertile layer or stroma is formed in the outer tissues of 

 the host as described by Magnus^ in C. krugiana, Magn. The mycelium grow- 

 ing luxuriantly in the parenchymatous and epidermal cells protrudes through 

 the outer wall of the latter and forms on the outside a dense mass of inter- 

 woven fungus filaments in the interior of which the spores are developed. 



The mass of hyphae closely compacted and felted together on the outside 

 constitutes the envelope or membrane together with the spore-forming hypha?. 

 The matrix from which the spores are formed adjoins the tissues of the plant, 

 and the older ripe spores are on the outside, while the inner and vounger spores 

 are towards the base. This spore -formation occurs in a radial manner, and 

 each row is separated from its neighbour by the mass of hyphai between , 

 which remains sterile. All the differentiated portions of the hyph;p of the 

 matrix do not grow to mature spores. A large number of them onlv form a 

 small cell cavity, and the gelatinous walls become swollen. The.}' appear later 

 to be absorbed, and probabh' supply material for the spores which grow 

 tx) nraturity. 



The successive production of spores in spore-bearing filaments, arising from 

 a so-called stroma, radiating outwardly and firudy agglutinated at inaturity, 

 is characteristic of Cintractia, but the sterile rays are not always present. 



SOROSPORIUM. 



In this genus the spores are in clusters and not separate and distinct as in 

 Ustilago. Fischer von Waldheini'^ has investigated their formation in 

 *S'. saponariae. Rud., and it is as follows : — The extremely abundant mycelium 

 in the blossom and ovary rapidly changes into spore-forming hvpha\ from 

 4 to 7 /( in dianK^tcr. and like those of Ustilago are gelatinous and full of sliining 



