THEORETICAL 187 



Apart from details Darwin, de Vries, and Weismann agree in ascribing as many 

 different pangens to the organism (biophores, physiological units, gemmules, 

 determinants) as it has of special organs and properties, whereas Nageli, Hertwig, 

 and others consider that a smaller number of pangens may be variously grouped 

 and associated together into systems of higher value, and ultimately into protoplasm. 

 In this way as many varied permutations and combinations are possible, as can 

 be formed of words and sentences from the twenty-four letters of the alphabet, or 

 of carbon compounds with oxygen and hydrogen. This view is more in harmony 

 with the facts of development, heredity, and variation, than that of Darwin and 

 Weismann, according to which only such properties and organs can be developed 

 for which an appropriate pangen exists, which when aroused directs and determines 

 the formative result produced. The gap between the two theories is partly bridged 

 over by supposing the specific determinants not to be absolutely stable, or to be an 

 aggregate of pangens formed under the given conditions. 



Since the specific determinants can apparently only act as stimuli, the result 

 produced must vary according to the character of the protoplasts affected, and to 

 produce a uniform result they must only be capable of acting when the protoplast 

 is in a specially attuned condition. If, however, the determinants are supposed to 

 be capable of attuning the protoplasts previously to stimulating them, then they 

 have properties possessed by no other living parts, as far as our knowledge goes. 



Darwin and Weismann suppose that the stimulating action is due to living 

 particles, specific pangens, which are either awakened from a resting condition in 

 the cell, or wander to it from other cells, whereas Sachs considers that a special 

 stimulating substance produced by metabolism is in each case responsible for the 

 formation of leaf, root, stem, and indeed for every form of growth '. These 

 leaf-, root-, and stem-forming substances need not, like the specific pangens, be 

 present in the fertilized ovum. Although all vital activity is based upon chemical 

 processes, and although chemical stimuli are of the utmost importance, this theory 

 involves a complete disregard of the mechanism of self-regulation, in which the 

 result is always due to the co-operation of various factors, and in which different 

 combinations including the same factor may lead to widely dissimilar results 2 . 

 Sachs' generalization is based upon a few specially striking instances of response to 

 chemical stimuli, and no evidence has ever been brought forward to prove the 

 existence of the special stimulatory substances postulated by him. Goebel supports 

 Sachs' view, whereas Vochting and others have shown that none of the instances 

 brought forward by Sachs bear the interpretation attached by him to them 3 . It 

 is therefore unnecessary to discuss the erroneous supposition that two dissimilar 

 stimulatory substances might be separated by the action of gravity, and so produce 

 the differentiation of stem and root. 



1 This is the later view put forward by Sachs (Flora, 1893, p. 236). The earlier view (Arb. 

 d. Bot. Inst. in Wiirzburg, 1880, Bd. II, p. 452 ; 1882, Ed. II, p. 689) that the formative influence 

 was due to the character of the food requires no discussion. 



2 Fatigue substances are not necessary for self-regulation. 



3 Goebel, Organography, 1902, I, p. 202; Vochting, Organbildung, 1884, II, p. 194; Jahrb. 

 f. wiss. Bot., 1885, Bd. XVI, p. 390; 1900, Bd. xxxiv, pp. 83, 107 ; Reinke, Jahrb. f. wiss. Bot., 1897, 

 Bd. xxxi, p. 262. 



