THAXTER. — 



MONOGRAPH OF THE LABOULBENIACEjE. 



223 



the host-integument from the foot itself, and arc .similar in all respects to the rhizoids developed from 

 the cells of the remarkable creeping secondary receptacles which characterize all the species of this genus. 



Although forms in which these organs replace the ordinary foot do not appear to gain any very ap- 

 preciable advantage as regards nutrition, at least in so far as is indicated by size or luxuriance, there can 

 be no doubt whatever that their function is one of absorption; since they arc thin-walled, with dense 

 protoplasmic contents, and arc not developed in such form as one would expect were their function 

 that of holdfasts merely. That they combine the office of holdfasts with that of absorbing organs is, how- 

 ever, manifest; since otherwise the individuals would be easily detached. Thus in Artkrorhynckus, 

 as indicated in figs. 2 and 7, Plate XLVIII, and in Ccraiomyrcs Dah/ii, Plate XLIII, figs. 3-4, a 

 somewhat abrupt swelling of the rhizoid immediately within the host-integument makes the removal of 

 an individual impossible without breakage, either of the host or of the parasite, and in Dimeromyces 

 rhizophorus the same end is attained by the abrupt divergence of the two branches to which the rhizoid 

 immediately divides on entering the body cavity. Cavara, in his paper above cited, criticises the writer 

 for having given scant attention to this matter of the method of food absorption, having apparently over- 

 looked such references as were made to the subject (Monograph, pp. 204-5). The theory advanced by 

 Cavara that the appendages are the organs of absorption, would seem untenable even were it not true 

 that appendages are sometimes wholly absent in these plants; since a majority of the forms come in no 

 immediate contact with water, except such as may be condensed on the surface of the host, and it is not 

 probable that the material necessary for the growth of chlorophylless plants rich in fat etc., can be taken 

 from the air. In general, too, the appendages are surrounded by the same impermeable membrane that 

 covers the other portions of these plants, and would appear to afford ineffective organs of absorption, 

 even were the surrounding medium a favorable one for obtaining food materials. The rigid limitation 

 of species of Laboulbeniales to single genera, or even species, of insects, which holds in general through- 

 out the group, could hardly, it would seem, be explained on a basis of pure saprophytism; and although, 

 as previously stated, the growth of these plants is not associated with any appreciable injury to the host, 

 it is nevertheless a true parasitism of a typically obligate type. In this connection it may be mentioned 

 that one ease has been observed in which definite injury is done to the abdomen of a soft bodied host. 

 The instance referred to, however, is not one in which the parasite possesses an intrusive haustorium; 

 but was seen in a number of the small flies parasitized by large numbers of Dimeromyces coarctatus. In 

 these cases a definite lesion, so to speak, appeared to be associated with the presence of the parasites, and 

 was indicated by a brown discoloration and by a shriveled condition of the parts attacked. 



The Structure of the Receptacle, although it is in general an uncertain guide in tracing general relation- 

 ships in the family and may in some instances vary very considerably in different species of the same 

 genus, or even in individuals of the same species, affords nevertheless characters of very considerable 

 diagnostic value. The large number of generic types herewith enumerated show so many variations and 

 combinations in this respect that it will not be possible in the present connection adequately to discuss 

 and compare them; yet certain of their types and general tendencies need to be mentioned, in 

 order that the conditions hereafter illustrated may be properly understood. It was formerly pointed 

 out in the earlier Monograph that the vegetative body of these plants, like that of the Red Seaweeds, is 

 in general reducible to a system of branching filaments which, in the present instance, is chiefly peculiar 

 from the fact that the system is, or tends to become, determinate in given genera and species, and that 



