26 THE AMERICAN NATURALIST [Vol. XLII 



parasitism and abnormal structures being developed after 

 germination. The remaining four groups are not only 

 deficient in structure at maturity, but they originate from 

 embryos which are also deficient in structure. The first 

 of those four groups to be considered is especially repre- 

 sented in our country by the genus Cuscuta which contains 

 many species, commonly known as dodder. They are 

 often found growing plentifully in fields, thickets and 

 waste places during the summer 

 months, their yellowish tangled 

 masses making them conspicuous 

 among the green vegetation. The 

 embryo of Cuscuta gets very lit- 

 tle sustenance from the albumen 

 which envelops it in the seed be- 

 cause the seeds are small; and it 

 is because the plants develop no 

 roots that they get no real nour- 

 ishment from the soil. Never- 

 theless, the plantlet grows rap- 

 idly, somtimes to several inches 

 in length, before it reaches a host; 

 and although it is so slender it 

 possesses great vegetative vigor. 

 This vigor is conspicuously ob- 

 servable in the subsequent growth 

 o f those species which often pro- 

 fusely festoon shrubbery, and 

 even trees, securing their hold upon, and their sustenance 

 from, the tender twigs by means of their haustoria. 

 Other species no less vigorously attack the smaller plants 

 and field crops with which they come in contact. 



The parasitism of Cuscuta* differs from that of the 

 other groups in being effected by climbing as a vine from 

 plant, to plant, and by lateral haustorial contact of the 

 stem and branches of the parasite with those of the host. 

 In the case of the other groups whose parasitism is above- 

 ground the success of the depredating plant depends upon 

 the propitious position which the seeds may accidentally 



