No. 494] 



PARASITIC PLANTS 



1D1 



it originated by any slow process, such as is generally 

 understood to be the case in natural selection. 



The mistletoes, which represent group 11. have reached 

 the condition of complete parasitism with less structural 

 and functional change than have any of the other recog- 

 nized groups. In view of the fact that they produce 

 their own chlorophyl, and that their structure is very 

 nearly normal, one can not doubt that they were origi- 

 nally normal phenogams, growing from the soil, although 

 they will not now grow there. As a family also, they are 

 now quite distinct from all other families, and as a group 

 of parasites they are so clearly separate from every other 

 group that one can not doubt that they have reached their 

 parasitic condition in an entirely different manner. Their 

 departure from the life-habit of normal phenogams evi- 

 dently consisted only of the transference of germination 

 and epitropism from the soil to the bark of trees ; while 

 the epitropic structure and functions, including both par- 

 turital and blastemal reproduction remained normal. 

 Unnatural and lacking in apparent incentive as has been 

 that transference, it is believed to have been suddenly 

 accomplished for the whole family, no trace of transi- 

 tional stages of parasitism having been discovered for 

 the species of either the Old World or the New. Although 

 the mistletoes are so nearly normal in structure, their 

 parasitism is as complete and heritable as is that of any 

 of the other groups. 



The European species, Lath ran aquamaria, which has 

 been chosen to represent group III, besides being distinct 

 from all other known parasitic forms, is, in a peculiar 

 manner, suggestive of the assumed suddenness with which 

 changes from normal to parasitic conditions have oc- 

 curred among phenogams. This species has five distinct 

 abnormal habitudes, which are repeated in succession in 

 every individual plant. Its germination is from an ordi- 

 nary seed in surface soil, and it is developed as a normal 

 plantlet from a normal embryo; but it soon abandons 

 itself to a remarkably diversified life. First, it produces 



