Kcproductivc Organs. 13 



do, and in this wav may convoy the discv.se to groat distanci^.s troin its 

 original source. The conditions favorable for the geriniiiation of the grain 

 are those most suitable for the germination of the spore, and it is, generally 

 speaking, the best time for the infection of the young seedling as well. 



In the case of Flag smut of rye or wheat, while a proportion of the spores 

 may be blown about by the wind, the greater number remain, attached to 

 the leaf, and when this withers up and falls away and becomes torn into 

 shreds, it not only forms a convenient means of dispersal, but pieserves the 

 spores in the soil until the next season, when they can infect the seedling 

 plant. The examination of commercial samples of wheaten cha:ff from 

 various parts of the State and the detection of spores of this smut in^ greater 

 or less quantity, show that this is a very efficient means of dispersion. 



Thaxteri regards it as very probable that insects may serve to spread the 

 spores, as in some other fungi, for he notes that the smut of Onions {Urocystis 

 cepulae) appears to be attractive to the " flea beetles," which swarm over 

 the diseased seedlings, and apparently feed upon the spores, while they do 

 not seem to visit the healthy onion leaf. 



Brefeld^ has observed that in some species the spores separate from one 

 another in water with a sort of jerk, as if some sort of intermediate substance 

 pressed them asunder, as in Cintractia spinificis, (Ludw.) McAlp. Probably 

 sweUing of the membrane, which occurs in spore-formation, also subse- 

 quently plays a part in spore distribution, but it may also be that the 

 mycelium left over after the formation of the spores retains the capacity for 

 swelling. 



Spore Formation. 



The spores are not formed from the ordinary mycelium, but at those spots 

 where the spores arise, the vegetative mycelium gives rise to special spore- 

 bearing iilaments. These filaments are produced directly as branches which 

 are quite distinct in their appearance and behaviour (Plate I., g-k). 



In connexion with the various genera, it is not only necessary to determine 

 the nature of the spores, but also the mode of their formation, for it is only 

 by means of such characters that the genera can be properly distinguished. 

 Hence it follows that each genus will require to be dealt with separately, 

 but a general view of the process may here be given. 



The spore-forming nlaments have their walls swollen in a gelatinous 

 manner, and contain a granular protoplasm in which a number of oleaginous 

 particles are often seen. This gelatinization of the walls of the filaments 

 is a fairlv constant character, but it does not occur in every species (Plate 

 I. e, f)/ 



The ordinary mycelium may change quite suddenly into the spore- 

 forming, as in Sorosporium saponariae, or it may be more gradual as in 

 TJstUago longissima, where the extremity of a filament may show the gradual 

 gelatinization and spore formation. 



When a filament is preparing for the process of spore-formation, its walls 

 beconie distended, while its cavity is diminished. Then the whole enlarges 

 together with the lumen, and the protoplasmic contents are ready to be 

 transformed into spores (Plate I., d). 



The spore is regarded by some authors as the result of a sexual process, 

 and it will be convenient to consider here the question of sexuality as 

 oc('urring in the Smuts. The evidence of sexuality is based upon the 

 behaviour of the nuclei, the presence of which is now firmly established in the 

 smuts, and not only so, but these nuclei are shown by Harper^ and others to 

 possess the same essential differentiations in structure that are met with 

 in the higher plants (Plate I., l-s). 



