lOO CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



at all. Certain it is that all the white redwoods I have seen 

 or heard of grow where the temperature is low in autumn 

 and winter. 



III. The Significance of the White Redwoods in 



Connection with our Conceptions of Parasitism 



AND of Heredity. 



White redwoods are wholly dependent, absolutely para- 

 sitic, plants which are in their first generation. They are 

 not the offspring of other white redwoods, they are not the 

 descendants of a long line of more and more dependent, 

 more and more degenerate, organisms. Their parasitic 

 characters have been acquired, or developed, during the 

 brief course of their own existence, but they possess some 

 parasitic characters not yet acquired by plants which have 

 been semiparasitic for no one knows how long. Phora- 

 dcndi'oii, Visaiin, and the other "green parasites" have 

 long lived at the expense of the other plants upon which 

 they grow; but though attached to their hosts, these para- 

 sites manufacture in their own green leaves their own non- 

 nitrogenous foods. 



As I have shown elsewhere (1893), the "green parasites" 

 which have been studied differ from completely parasitic 

 flowering plants (e. g. Ctcscuta, Brugmansia, Raff,esia) in 

 the completeness of the connection between the tissues of 

 host and parasite effected by the haustoria. In the com- 

 plete parasites, xylem and phloem of the parasite are directly 

 connected with the xylem and phloem of the host by means 

 of xylem and phloem tissues which are continuous through- 

 out the haustoria. In the "green parasites," on the other 

 hand, only the xylems of host and parasite are directly con- 

 nected. This anatomical difference may be considered the 

 reason for the difference in the degree of parasitism in 

 these two sets of plants, or we may conceive that, so long 

 as the parasite remains green, and therefore able to manu- 

 facture its own food, a complete connection with both 

 sets of conducting tissues in its host is unnecessary and 

 unformed. There is at present no means to decide which 



