Morphology. 39 



spore^ there is frequently present a layer external to 

 the epispore, whicli is in reality a continuation of tlie 

 wall of the parent hypha, the true spore with its own 

 cell-membrane, composed of epispore and endospore, 

 being differentiated within the hyphal wall. This ex- 

 ternal membrane De Bary calls the j)rimaY\j laviella. 

 In addition to the membranes already described, 

 many spores, both acrogenous and ascospores, have a 

 gelatinous outer layer, which swells up in water and 

 eventually disappears. This gelatinous substance, in 

 the case of many ascospores, forms variously shaped 

 appendages to the spores. Its origin is uncertain. In 

 coloured spores the colour is usually confined to the 

 epispore, which may be smooth or variously orna- 

 mented with warts, spines, or ridges, the latter 

 frequently anastomosing to form a reticulation. The 

 endospore is smooth and usually colourless. Some 

 spores have pits in their membrane, which in many 

 species serve as places of exit for the germ-tubes 

 during germination, and are called c/erm-pores ; in 

 other instances these pits serve no known function. 



Nuclei, as already stated, have been demonstrated 

 in many spores, but the term nucleus as used by 

 systematists refers to drops of oil or some fatty matter, 

 and disappears on the application of dilute hydrate of 

 potash. The dispersion of spores is effected in various 

 ways. A common method in many Ascomycetes is as 

 follows : — when the spores are mature, the wall of the 

 ascus, which is elastic, becomes considerably extended 

 by a constantly increasing quantity of watery fluid. 

 This expansion is most marked in the upper half of 

 the ascus^ and when the wall has reached its maximum 



