60 BULLETHSJ" 957^ IT, S. DEPAETMEISTT OE AGKICULTURE. 



Germination of fresh urediniospores usually takes place readily in 

 tap water. Gravatt found that distilled water gave poorer germina- 

 tion than tap water. CoUey (20) found that the germ tube pushes 

 through the exospore without the aid of a germ pore. The contents 

 of the spore soon pass into the young germ tube, which may extend 

 some distance over the surface of a Ribes leaf. Entry to the interior 

 of the leaf appears to be through the stomata. The urediniospores 

 germinate in about five and one-half hours (28) in drops of distilled 

 water on glass slides. 



During germination studies m 1918, York ^^ occasionally found 

 germinating urediniospores which formed secondary conidia. An in- 

 vestigation of the conditions causing their formation showed that 

 newly formed urediniospores usually do not produce the secondary 

 conidia in tap water, while old urediniospores were more likely to 

 produce them. The following species produced them, the frequency 

 increasing in the order named: Ribes lacustre, R. cynoshaii, R. vulgare, 

 R. reclinatum, and R. nigrum. Urediniospores from R. glandulosum 

 did not produce secondary conidia. Urediniospores exposed in bags 

 of mosquito nettmg out of doors gave' especially abundant secondary 

 conidia. Urediniospores from R. nigrum produced secondary conidia 

 in weak solutions of ammonia, maltose, tannic acid, gallic acid, malt 

 extract plus gallic acid, lactose plus tannic acid, and lactose plus 

 gallic acid. They were especially abundant in the last solution. 

 They were not produced in pine decoction, weak solutions of ether, 

 lactose, maltose plus tannic acid, and maltose plus gallic acid. A 

 limited number were produced in water. They form on the ends of 

 the germ tubes or laterally and are capable of producing a germ tube 

 themselves. Similar secondary conidia have been noted by Tulasne 

 (175) in cultures of Cronartium asclepiadeum, and they have been 

 noted by Plowright (109) and Sappin-Trouffy (122) in other Uredi- 

 nales. 



LONGEVITY OF THE UREDINIOSPORES. 



The first experiments in testing the longevity of urediniospores of 

 Cronartium rihicola seem to have been carried out by McCubbin ^^ in 

 1916. His manuscript account of these experiments follows: 



The spores used for this series were all collected on the same day. They were dried 

 on paper for a few hours and then placed in a number of small bottles plugged lightly 

 with cotton, the contents of each bottle being available for a single inoculation. 

 Half of these bottles were kept on a shelf in the laboratory, where they were dry and 

 exposed to weak light, and the other half were placed under a bell jar on the soil 

 in a garden, exposed to changes of humidity, temperature, and light. 



At stated intervals a bottle was taken from each set and the spores within were 

 shaken up mth a small amount of distilled water. By the use of a small atomizer 

 the suspension of spores was then sprayed on the under side of the leaves of small 



38 York, H. H. Op. cit. 



33 McCubbin has very kindly allowed the use of his unpublished data so as to make this account as com- 

 plete as possible. 



