Morphology and Life-History 9. 



spring following the season in which the perithecia were produced. 

 In some cases, as in Eyysiphe galcopidis, and, as a rule, in E. 

 grauiinis, the ascospores are not formed until the following spring, 

 the protoplasm of the asci remaining throughout the winter in a 

 granular condition. It appears that the ascospores are incapable 

 of immediate germination, and require to pass through a resting 

 stage, lasting the winter months. Galloway (139) and also 

 Worthington G. Smith (329) state that in the spring the perithe- 

 cia, under favorable conditions, suddenly burst and forcibly eject 

 the asci. Harper (161, p. 663) mentions that the cells of the inner 

 wall of the perithecium permanently retain their nuclei and proto- 

 plasmic contents, and suggests that they may produce a substance 

 capable of swelling in water, and so causing the rupture of the 



r 



perithecium. 



The ascospores In a damp atmosphere or in water send out in 

 a few hours germ tubes, which (according to Wolff) on reaching 

 the epidermis of a suitable host-plant penetrate and form a haus- 

 torium, from which center the ordinary vegetative mycelium is 

 produced. Very little, however, is known on the subject, and no 

 records exist, apparently, of any artificial infection of host-plants 

 by means of ascospores. Galloway ( 1 39) has made some valuable 

 observations on the ripening and germination of the ascospores in 

 Uncimda necator and Wolff (398, 399) i" the case of Erysiphe 

 grmninis, and Tulasne has recorded cases of the commencement 

 of germination of the ascospores of Phyllactinia cotylea, Sphae- 

 rothcca pannosa'-dwA Erysiphe tor tilts. '■ 



With the formation of perithecia the mycehum frequently en- 



tirely disappears. 



Sphaerotheca pannosa 



and Erysiphe graminis, it is persistent, and produces special 

 branches in the form of long, branched, interlaced, shining, thick- 

 walled hyphae, in which the perithecia are more or less immersed. 

 It has been stated that in certain species, viz, Sphaerotheca pannosa, 

 Podosphacra oxyacanthac, P. leucotricha and Uncimda necator, the 

 mycehum is perennial, passing the winter months in a state of hi- 

 bernation ; definite proof of- this, however, has not been given in 



any case. 



It is sometimes found that perithecia, which externally present 

 the normal appearance, instead of containing asci, emit when opened 



