g Reproductive Organs. 



The influence of various chemical substances on germination has been in - 

 vesLate^ and t has been found that some substances, such as solutions 

 of su g gar and nitrate solutions, hasten germination ; but for general purposes 

 water alone is all that is necessary. Sometimes, however the spores will 

 germinate and infect the leaves of the host-plant, although they may nol 



d Freema^'found this to be the case in dealing with the uredo-spores 

 of Puccinia bromina, and concludes that the negative results in distilled 

 water tests are not always an indication that the spores are incapable of 

 germination. The temperature seems to exercise an important influence^ 

 Eriksson found that in many cases the spores germinated more freely if 

 previously exposed to a temperature of o deg. C. or under and Marshall 

 Ward that the uredospores of P. bromina were not injured by being ex- 

 posed' to a temperature of - 5 deg. C. for ten minutes while the same tem- 

 perature continued for four to five hours killed them. Heat or cold, drought 

 or damp, age and ripeness, are all factors of importance in germination. 



DURATION OF GERMINATING POWER. 



How long do the spores retain their germinating power is an important 

 question to settle; but not many definite determinations have been made. 



De Bary states that the uredospores of P. gramims, kept dry, lose their 

 germinating power in one to two months. 



Marshall Ward found that (the uredospores of P. bromina preserved dry 

 for sixty-one days retained their germinating power ; but it was feeble. 



Barclay found certain uredospores still capable of germination after 

 from two to eight months, the leaves on which they occurred being kept 

 dry. 



'it is a question of great scientific interest in connexion with rust in 

 wheat if the uredospores can retain their germinating power during the 

 winter. The results vary, ajs might be expected, according to the condi- 

 tions prevailing at the time. In contrast to De Bary's results, Eriksson 

 found that the uredospores of P. graminis lost their germinating power 

 during the winter if kept in the open, but retained it if kept inside. 

 Hitchcock and Carleton 1 , however, collected fresh uredospores from 

 growing plants of P. rubigo-vera at various times during the winter, and 

 found them capable of germination. In our comparatively mild winters 

 the uredospores retain their power of germination, and this seems to be the 

 means whereby the fungus is continued from season to season. I have 

 had freshly gathered uredospores of P. graminis from growing wheat and 

 oats, and P. triticina from wheat germinating freely in water in winter 

 (June to August). The uredospores can germinate at once, and directly 

 infect the host-plant, or they can act as resting spores for a time, and 

 freely infect the next season's growth, under the climatic conditions which 

 prevail here. 



The germination of teleutospores takes place ait different periods, ac- 

 cording to the nature of the species. They may either germinate imme- 

 diately on reaching maturity, or, as is the case in the majority of heteroecious 

 lusts, only after undergoing a period of rest in the old world usually in 

 the winter, but here, as no doubt sometimes elsewhere, the period of rest 

 is often partly in the summer, when drought checks growth as effectively 

 as the cold of a European winter. 



Eriksson 10 has shown that the teleutospores of P. graminis, with few 

 exceptions, only germinate in the spring following their formation, and 

 only then if kept in the open during the winter. He kept spores in the 

 herbarium for one or two winters, and then on exposing them for another 

 winter, he found that they germinated, but this was exceptional. 



