104 THE AMERICAN NATURALIST [Vol. XLII 



tion of the parasitic characters of group IV, or of the 

 manner of its world-wide distribution. 



v As is the case with the other groups which are herein 

 mentioned, nothing is known of the pre-germinative his- 

 tory of the characteristics of group V. The members of 

 this group belong to a noted family of parasitic genera, 

 the Orobancheae, of which the destructive broom-rapes 

 are among the best known examples. They all begin life 

 in a simple, filiform embryo, which is not only without 

 differentiation into cotyledons, radicle and plumule, but 

 which is also extremely abnormal in its method of germi- 

 nation. The members of group V, like those of group 

 IV, are annuals. As regards the structure of the seed 

 and embryo and the initial conditions of germination, the 

 members of both groups are similar, but their results are 

 extremely different. The germinating offshoot of the 

 former springs upward, sending no root into the ground, 

 but seizing upon the growing parts of its companion 

 plants by its haustoria. The offshoot of the latter bur- 

 rows downward and seeks a root-host, failing to find which 

 it dies without producing any upward growth. Finding 

 a root-host, a substituent plantlet is developed from 

 their conjoined parts which rises above ground, producing 

 flowers and seed. The physical structure of the embryo 

 of both plants is identical, and both are abnormal. Im- 

 mediately upon germination the great differences between 

 the plants appear, but neither in those differences or 

 in their common embryonal structure is there any sug- 

 gestion of a community of origin with each other, or with 

 any other plants. 



A leading characteristic of all the forms of phenog- 

 amous parasitism is the permanence and heredity of their 

 attributes. Increasing abnormality of structure and habit, 

 however, is suggested, but not proved, by the members 

 of group VI, which is represented by the Eafflesias and 

 some closely related genera. The conception which one 

 naturally forms of a phenogam that may have been the 

 normal ancestor of these plants is one having root, stem, 



