Darivins Pauycncsis. 633 
enormous amount of literature which has since accumu- 
lated on this subject, 1 and with regard to the older the- 
ories, such as those of SPENCER,, NAGELI and HERTWIG, 
I need do no more than refer to my essay already quoted. 
My only task is to show that the evidence, brought for- 
ward in this book for the theory of mutation, affords 
a strong suport for the principle of pangenesis. All that 
is necessary to bring the results of observation into line 
with the doctrine of Pangenesis, is to substitute the idea 
of internal factors or material vehicles of hereditary 
characters for the empirical units of the visible qual- 
ities. 2 This view has been best worked out by JOH ANN- 
SEN in the section on the doctrine of pangenesis in his 
textbook of botany which has recently appeared; and 
this fact enables me to deal briefly with the topic. 3 I 
propose to confine myself to a brief exposition of DAR- 
WIN'S conception of pangenesis and to the modification 
of it which I suggested, without repeating all the obser- 
vations on the subject which I have recorded in this book. 
I shall deal first with the essence of the hypothesis and 
then with the secondary hypotheses ; and shall defer a dis- 
cussion of the essence of the theory until later. 
There are two essentially different views relating to 
the material vehicles of the hereditary characters of or- 
ganisms. One view is that of SPENCER, according to 
1 Full lists of references are given in a large number of works 
of which the following are among the best: C. KELLER, Vercrbungs- 
lehre und Tlriersucht, 1895; H. MARLIERE, Etudes sur I'hcrcdite, 1895; 
E. B. WILSON, The Cell in Development and Inheritance, 1900; FRU- 
WIRTH, Die Zilchtung der landivirthschaftlichen Culturpflansen, 1901, 
etc. 
2 Bcr. d. d. bot. Ges., 1900, XVIII, p. 83, and Sur les unites des 
caractcres s[>c cinques, Revue generate de botanique, 1900, XII, p. 257. 
3 E. WARMING and W. JOHANNSEN, Den almindclige Botanik, 4th 
ed., 1901, pp. 675 ff. It is quite satisfactory to state here that several 
critics of the first volume of my book have anticipated this conception 
of the relation of the doctrine of mutation to pangenesis. 
