,14 MASSACHUSETTS HORTICULTURAL SOCIETY. 



eight miuute spores, which upon germiiiatiou produce a mycelium 

 and spores, thus completing the cycle. Each of these little sacs 

 thus born in a special receptacle is called an ascus, and the spores 

 within them are called ascospores to distinguish them from the 

 aerial spores or conidia. 



Here then we find the typical characteristics of the large group 

 of ascomycetous fungi — usually of very small size — a vegeta- 

 tive system of delicate tubes or hyphae, branching and interlacing 

 to form a mycelium which is usually buried in the substance of the 

 substratum ; and a reproductive system consisting of minute 

 bodies called spores, born either free in the air, on specialized 

 branches of the mycelium, or contained in sacs called asci, which 

 in turn are enclosed in special receptacles composed of the 

 adjacent hyphoe modified in form and generally indurated. 



I have spoken of a seemingly sexual process of fertilization as 

 giving rise to the ascus-bearing spiral. This condition is 

 undoubtedly typical of the Ascomycetes, but can no longer be 

 considered as normal. In the vast majority of cases the 

 ascospores and their receptacles are formed with no intervening act 

 of fertilization, and it is not difficult to trace the general trend of 

 development in the group. The ascospores are as a rule born 

 in comparatively small numbers ; they mature slowly, but are 

 correspondingly resistant to unfavorable surroundings. The 

 aerial spores or conidia on the other hand are produced in enormous 

 numbers and are short-lived, but this latter condition is com- 

 pensated for by the fact that they reach maturity very quickly and 

 germinate within a few hours if the conditions are favorable. It 

 is therefore by these means that fungous diseases are enabled to 

 spread so rapidly. Moreover these spores are so minute as to be 

 readily conveyed, sometimes for miles, by the wind, currents of 

 water, or insects. We recognize then a distinct tendency through- 

 out the group towards a repression first of sexuality ; then of 

 the slowly maturing, resistant ascospores, and the replacement 

 of the latter by enormous quantities of delicate spores, borne free in 

 the air, whence they can be carried in all directions, requiring but a 

 short time for development, and germinating as soon as mature. 

 It is an evolution toward quantity rather than quality, a fact of 

 immense importance in the economic study of fungi. There are 

 at least two other forms of spore which the typical ascomycetous 

 fungus produces. Like the ascospores they are borne in closed, 



