32 Transactions. 



pounder of that theory), I have found it necessary, in order to account for 

 the facts which have passed under my own comparatively limited observa- 

 tion, to assume, as a postulate, the derivative origin of species, and to 

 accept with little reservation the explanations afforded by the theory of 

 " descent with modification by means of natural selection." Now, at the 

 time I wrote to Dr. Hooker, I had, partly as the result of reading and partly 

 from observation, arrived at certain opinions on the subject of plant varia- 

 tion, which may be stated in the following propositions : — 



1st. That certain classes of plants exhibit a greater tendency than others 

 to acquire modifications as the result of changes in the conditions of life. 



2nd. That variation resulting from this cause may be sudden, or may 

 result slowly from the operation of this cause acting continually and regularly 

 upon the same species in the same locality. 



3rd. That the acquired modifications will be transmitted to posterity 

 whether acquired suddenly or slowly. 



4th. That, under domestication, variation exhibits itself the more readily, 

 because the plant is usually subjected to a more rapid succession of changes 

 in the conditions of life, many of which are specially applied analogically in 

 order to produce some particularly desired result. 



In arriving at these general conclusions, I assumed that the f ertiKzed ovule 

 is essentially a bud, and that it embodies to the fullest extent, and is a per- 

 fectly natural expression of, all the incidents, if I may use the term, for the 

 time being acquired by the parent plant. The actual condition of the fertilized 

 ovule and bud has recently been the subject of a provisional hypothesis 

 by Mr. Darwin, termed Pangenesis, in his great work on the subject of 

 Variation under Domestication, in which he supposes that the Avhole 

 organization, in the sense of every separate atom or unit, reproduces itself 

 — ^that each ovule or bud, as the case may be, is an absolute epitome of the 

 whole parent organism, or, to use his own words, " includes and consists of 

 a multitude of germs thrown off from each atom or unit of the organism." 

 The assumption which I ventured to make in my communication to Dr. 

 Hooker had reference, however, to the offspring of a single species only. 



In the production of hybrids, or the offspring of two different though 

 allied species, on the other hand, I conceive that a violence is done : that 

 an attempt is made to fuse together two organisms each of which has, for 

 the time being, acquired all the modifications necessary to enable it to con- 

 tinue the struggle for existence under the peculiar conditions of life to 

 which it is exposed, even though ultimately destined to disappear before 

 some more powerful type. The result of such a union, therefore, would be 

 that the fertilized ovule would produce a plant partaking of the character 

 of both parents, accompanied by a tendency to eliminate the characters 



