36 The Unity of the Organisin 



titled The Nature of the Plant. After illustrating the prin- 

 ciple of symbiosis by referring particularly to the case of 

 the mutually dependent combination existing between the 

 flat-worm Convoluta roscoffensis and a green alga, recently 

 well studied by Keeble and Gamble, ]Mr. Davidson goes on 

 to argue that if a typical plant, a tree for example, be 

 considered to be a like symbiotic complex, "much that 

 has been dark in the vegetable world becomes clear."^ 



The members of the partnership in the plant so con- 

 ceived would be the flowers, equivalent to the "hermaphro- 

 dites and males and females" occurring in the world of in- 

 sects, and the buds equivalent to the underdeveloped females' 

 or neuters. Among the darknesses enveloping plant life 

 which the autlior believes would be illumined by this theory 

 he mentions that of the plant's individuality. In the light 

 of the theory it becomes obvious, the author holds, that a 

 "plant is not, as is generalh^ supposed, an individual entity, 

 but in reality a group or family of individuals, associated 

 within a common protecting envelope, the bark, and upon a 

 common root for the common good."^ These "associated 

 individuals" Mr. Davidson calls plantagens since, he says, 

 "they cannot well be written about unless they have a name." 



Another meritorious thing about the plantagen theory, 

 its inventor believes, is that it removes the difficulties in the 

 way of the germ-plasm theory of Weismann, presented by 

 plants. The type of reasoning which has given rise to this 

 rather ingenious speculation will receive due attention in 

 various parts of this volume. I bring up the case here only 

 as a specific instance of "certain general tendencies to er- 

 roneous reasoning" above referred to. There is always the 

 inclination to ascribe more casually interpretative value to 

 some of the parts of organisms in their relation to other 

 parts and to the whole than actually belongs to them. In 

 the present instance this effort is seen in the fact that both 

 the asexually and sexuall^'^ propagating elements of any 



