THE GERM-PLASM THEORY 385 



minants ' any more than there are ' zigzag determinants ' or ' crooked 

 nose determinants,' but there are determinants controlling the nature 

 of the cells which give rise, under normal conditions of development, 

 to the straight stem, under abnormal conditions to the zigzag stem, or 

 to a flat nose instead of a crooked one, and so on. 



This consideration should make it clear that plant-galls are not 

 in the remotest degree a stone of stumbling for the determinant 

 theory, as some have supposed. Of course there can be no 'gall- 

 determinants,' for galls are not transmissible adaptations of the plants 

 on which they occur ; they arise solely through the larvse of the gall- 

 insect which has laid its eggs within the tissues of the plant. But 

 the specific nature of the difierent kinds of plant-cells, predetermined 

 by their determinants, is such that, through the abnormal influences 

 exercised upon them by the larvae, they are compelled to a special 

 reaction which results in the formation of galls. It is marvellous 

 enough that these abnormal stimuli should be so precisely graded and 

 adjusted that such a specifically definite structure should result, and in 

 this case there is obviously a very different state of matters from that 

 obtaining in most other processes of development, in which the chief 

 determining factor is rather implied in the nature of the idioplasm, 

 that is, of the determinants, than in the nature of the external 

 influences. Here, however, the specific structure of the gall depends 

 mainly on the quality, variety, and successive efiects of the external 

 influences or stimuli. In discussing the influences of surroundings 

 I shall return once more to the galls. 



My determinants have generally been regarded as if they were 

 like grains of seed, from which either nothing may arise, under un- 

 favourable conditions, or just the particular kind of plant from which 

 the seed itself originated. 



This simile is, however, to be taken cum grano salts. The whole 

 ovum is certainly comparable to a grain of seed, but single deter- 

 minants or groups of determinants will always be able to adapt 

 themselves to difierent influences, and to remain active even under 

 slightly abnormal conditions, though in that case the resulting 

 structures may be somewhat divergent. This relative plasticity is 

 indispensable even in relation to the ceaseless mutual adaptations of 

 the growing parts of the organism. Not only do the cells which live 

 beside each other at the same time influence each other mutually, but 

 the influence extends to the whole cell-lineage. No cell or group 

 of cells develops independently of all the others in the body, but each 

 has its ancestral series of cells on whose determinants it is so far 

 dependent, since these have taken part in determining its own nature, 



