172 



PYRENOMYCETES 



[CH. 



contain oil globules. Between adjacent cells that have the same origin the 

 protoplasm is continuous through broad pits. The cytoplasm on each side 

 dips into the pit, forming a thick strand which, in Laboulbenia at least, appears 

 to be intersected by the middle lamella (Faull). The latter in favourable 

 cases is seen to be perforated by one or more fine pores through which com- 

 plete continuity is established 1 . There is evidence that a stout strand of 

 cytoplasm unites contiguous cells in the appendages. 



The spores are remarkably uniform throughout the group, being in- 

 variably hyaline and fusiform or acicular in shape and almost invariably 

 two-celled (fig. 132). The cells are commonly of unequal size, that nearest 

 the apex of the ascus being the larger, and both 

 are uninucleate. The spore is clothed in a gelati- 

 nous sheath especially well developed about the 

 upper end which, when the spore is discharged 

 from the perithecium, is destined to come in con- 

 tact with the integument of the host. Here the 

 gelatinous mass enables the spore to take up the 

 oblique position in which germination occurs. 



The lower extremity of the spore (its apex 

 while in the ascus) forms the foot. As a rule the 

 gelatinous envelope in this region becomes hard, 

 opaque, black and more or less elastic and thus, 

 while adhering firmly to the substratum, it may 

 give the plant a certain freedom of movement. 

 This elasticity is found especially in forms on sub- 

 merged and rapidly swimming hosts where it 

 allows the parasite to lie back along the body 

 of the insect. Sometimes the foot is cut off from 

 the rest of the plant by a wall, more often it is continuous with and forms 

 part of the basal cell of the receptacle. In the great majority of cases it 

 does not penetrate into the substance of the host but is in contact with 

 the surface by a thin membrane through which materials are absorbed into 

 its cavity. 



here are a certain number of forms, however, especially those occurring 



on soft-bodied insects or on the soft parts of others, in which a definite 



izoidal apparatus is developed and penetrates the body of the host. These 



s show no greater vegetative luxuriance than other members of the 



group and apparently do not benefit by their more elaborate absorptive orga.n 



The receptacle, like the foot, develops from the lower segment of the 



isists, m the simplest cases, of two superposed cells and (in 



off for the Red Algae <" Neue 



Fig. 132. Laboulbenia elon- 

 gata Thaxter ; bicellular 

 spore; after Thaxter. 



