1892.] NATURAL SCIENCES OF PHILADELPHIA. 383 



The conclusion left on the mind of the observer was that some 

 plants of the radish were arranged for self-fertilization, and others 

 required the intervention of insects, but that this so-called 

 " arrangement " was brought about through various phases of nutri- 

 tion affecting the growth of different portions of the plant, and in 

 which special arrangements for fertilization had no primaiy place. 



On the Nature of the Verruca in Some Convolvulace^. 



The stems of some Convolvulaceie, notably the one in common 

 cultivation as " ]Moon-flower " ( Calomjction speciosum Choisy, Ipomcea 

 Bona nox Linnaeus), are verrucose. No explanation of the nature or 

 functions of these warty processes has ever been given, so far as the 

 knowledge of the writer extends. Horticulturists who have given 

 any thought to the matter have regarded them in the light of 

 attempts at root formation or as somew'hat akin to the rootlets along 

 the branches of ivy ; but these have been only passing impressions. 

 A critical examination, however, shows that they have no central 

 system, as true rootlets have, nor have they a root-cap, as we find 

 on genuine fibres. 



It occurred to me to note the behavior of Cuscuta, when grow- 

 ing where it could not readily find a host plant. It produces haus- 

 toria ready to fasten on its victim when the opportunity might offer. 

 The structure of these processes and those of Calomjction seem 

 identical. As it must be conceded that Cuscuta is a genus of 

 degenerate Convolvulacere, or rather a genus of plants that has 

 come in the course of ages to be able to live on other plants, it does 

 not seem improbable that these seeming excrescences on the Calo- 

 nyction may' be incipient haustoria, and that in the future other 

 Convolvulaceffi besides Cuscuta may become parasitic. It must be 

 said, however, that in many examinations I have made where these 

 supposititious haustoria have been brought into close contact with 

 other growing vegetation to such an extent, in some instances, as 

 not to afford room for the usual longitudinal development, the 

 excrescences have become flattened rather than make any attempt 

 to penetrate the tissue of the approximating plant. This, however, 

 may not militate against the supposition that these warty excres- 

 cences are incipient haustoria, unless the proposition that in plants 

 environment, or more properly, perhaps, environment to a great 

 extent, is the leading factor in the evolution of characteristic forms. 

 Such a proposition, to my mind, implies that the change in form 



