MONOGKAPII OF THE LAIiOULHENlACEyE. 



205 



IV, figs. 1 and 3) the basal cell sends into the body cavity of the host a copiously 

 branched and well-developed rhizoid-like organ, the interior of which is apparently 

 continuous with that of the basal cell. 



In cases where a typical foot is formed, it may constitute a cell distinct from the 

 basal cell of the individual, as is at least often the case in St!(jmatom/jce$ Bceri (Plate 

 I, fig. 14), a condition which may very likely exist in many other instances, although 

 obscured by the blackening already mentioned. In some instances this blackening 

 involves more than the basal cell of the mature plant, as in some species of Cerato- 

 myces (Plate XXV, figs. 15 to 17). 



In forms like those just mentioned in which a definite haustorium is present, it is 

 quite evident that this organ constitutes the means by which the parasite absorbs 

 from its host the nourishment necessary for its growth, and at the same time serves 

 to fasten it securely. In the great majority of instances, how r ever, it is probable that 

 there is no intrusion of any kind from the ordinary form of blackened foot into the 

 substance of the host. That this is the case may be clearly seen in preparations in 

 which the parasite is shown attached to some transparent portion of the host's integu- 

 ment, as in fig. 4, Plate III. In the specimen here represented several individuals 

 were fixed to the surface of the thin integument of one of the abdominal segments of 

 the host, the substance of which was perfectly transparent, so that by inverting the 

 piece to which they were attached, so as to view its lower surface, one could observe 

 with accuracy the relation of the adherent portion of the foot to the chitinous surface 

 to which it is applied. In such a specimen it is evident that this sucker-like adherent 

 portion consists of a flat area in the closest contact with the chitin of the integument, 

 and consisting of a thin membrane through which the absorption of nutriment takes 

 place, bordered, as in the figure cited above, by the thick base of the indurated exter- 

 nal wall of the foot proper. It should be mentioned, however, that Peyritsch figures 

 sections of a fly's integument which indicate a slight penetration through the pore 

 canals in the case of Stigmatomyces. 



In addition to its function of attachment and absorption the foot may, in some of 

 the aquatic genera more particularly, perform the office of a fulcrum on which the 

 plant is supported and by means of which it is allowed a certain freedom of motion 

 which it could not otherwise attain. This is effected through the more or less sudden 

 and distinct enlargement of the foot above its point of attachment. The rounded ful- 

 crum thus produced rests on the surface of the host, allowing the body of the plant, 

 although appressed, to lie free from the insect and to roll upon it from one side to the 

 other, as far as the elasticity of the attached portion will permit. This is most clearly 



