HELIOTROPISM OF ASCI IN DISCOMYCETES 299 



bulged out laterally so as to attain diameters often of 12-16 (jl 

 (Vol. I, Fig. 79, D, p. 241). The lateral expansion of the shaft-cells 

 of the paraphyses under moist conditions of development is one of 

 the factors which cause a fruit-body to open out hemispherically 



Fig. 145. — Aleuria vesiculosa. Heliotropism of parapliyses. Median-vertical sec- 

 tion of the side of a young fruit-body : a, cortex ; b, hypotheciuin ; c, hymenium 

 made up of long slender paraphyses and of young asci pushing outwards and 

 upwards between the paraphy.ses. The paraphyses, which developed before 

 the asci, have become heliotropically turned toward the source of light and 

 therefore upwards as indicated by the arrows. The asci, which are not yet 

 half -grown, are straight and have not yet begun to bend toward tlie source of 

 light. The heliotropic curvatures which the asci will make will coincide in 

 direction with those already made by the paraphyses. Magnification, 293. 



or, in the laboratory, to become flattened and even recurved over 

 the substratum. The asci do not all begin their development at 

 the same time nor do they all attain maturity at the same time, 

 but some have the start of others. In the laboratory, and doubtless 

 also under natural conditions, the fruit-body may discharge spores 

 several times in succession by puffing. When the first set of ripe 

 asci has discharged its spores, the paraphyses swell up laterally and 



