36 ERYTHEA. 



plant penetrating only through the outer covering of the insect by 

 a short process. Consequently they do not figure as insect enemies^ 

 and have little or no economic interest. 



The spores are borne in asci, are two-celled, and are invested at 

 maturity by a gelatinous covering which helps them in adhering to 

 the insects with which they come into contact. When the spores 

 germinate they become attached by one end to the insect and 

 grow out into a more or less complex plant body. Professor Thaxter 

 distinguishes the receptacle or supporting part of the plant body 

 thus produced, from the perithecia and from the appendages which 

 bear the antheridia. The receptacle possesses at the proximal end 

 a small blackened organ, the foot, which penetrates the body of the 

 host and draws nourishment from it through the tip, where a small 

 circular portion of the investing membrane is much thinner than 

 elsewhere. 



The perithecia are produced as lateral branches from the tissue 

 derived from the activity of the proximate cell of the spore. Each 

 perithecial branch is at first a single cell, which soon becomes two, 

 through the formation of a horizontal septum. The lower cell 

 forms the perithecial wall, while the upper cell forms the procarpic 

 branch. The latter consists of three superposed cells, designated 

 thus: a basal or carpogenic cell, a middle or trichophoric cell, and 

 a terminal cell, which grows out into a trichogyne. The trichogyne 

 may be simple and unicellular, or it may be divided into a number 

 of cells, and even branched, after a very complicated fashion. Such 

 trichogynes are receptive, however, only at the tips. 



The antheridia are borne upon the appendage and are always 

 produced from the cells arising from the distal cell of the spore. 

 In a few aquatic species the spermatia are abjointed directly from 

 lateral branches of the appendage, but in the majority of the species 

 they are produced inside flask-shaped cells, from whose necks they 

 issue singly. 



Fertilization takes place through the copulation between a sperma- 

 tium and the trichogyne, after which the trichogyne withers and the 

 carpogenic cell begins to divide by horizontal septa until three 

 superposed cells are formed. The two lower cells take no farther 

 part, but the upper one divides by oblique divisions into from two 



