ARE ACQUIRED CHARACTERS HEREDITARY? 337 
plasm.”’ According to this view as brought out by Professor Guyer 
(p. 296), there is an unbroken continuity from generation to generation 
of the germ plasm. Germ cells are thought of as remaining entirely 
undifferentiated for any somatic function and as therefore capable of 
starting at the beginning to.develop a new individual. The germ cell 
is supposed to be “set apart at an early period in a given individual, 
it takes no part in the formation of the individual’s body, but remains 
a slumbering mass of potentialities which must bide its time to awaken 
into expression in a subsequent generation.” 
Physiologists object to this idea that the germ cells are so dis- 
tinctly different from body cells and that they are so insulated, as it 
were, from the soma as to be immune to any changes that may affect 
the latter. Two kinds of data are offered in opposition to this con- 
cept. A few observers, notably Professor C. M. Child, have described 
cases in which somatic cells, that already had become differentiated 
as primitive muscle cells, lost their differentiation and returned to a 
germinal condition. If this kind of thing were general, and it is 
probably not, germ cells might conceivably be produced from func- 
tioning soma cells and might therefore furnish a mechanism for the 
transmission of the effects of use and disuse. It should be empha- 
sized, however, that, among animals at least, there is extremely little 
evidence in support of the idea that differentiated body cells give rise 
to germ cells. 
Among plants, however, a different situation prevails. In the 
Begonia, for example, any part of a plant if cut off is capable of pro- 
ducing a whole new plant. Even a purely vegetative organ like a leaf, 
if cut off and partially buried in soil, will bud off a new plant which 
will produce flowers with perfectly typical germ cells. We have to 
admit, in this case, either that leaf tissues contain undifferentiated germ 
cells or that somatic tissues give rise to germ cells. The first alterna- 
tive is in harmony with the germ-plasm hypothesis, the second is 
the preferred view of the opponents of this hypothesis. 
Among animals, as for example annelid worms, it is quite common 
to find the germ cells aggregated in a few segments of the body. Ifa 
part of the body in which there are no recognizable germ cells be cut 
off, it will, under proper conditions, regenerate the lost parts and 
become a complete worm with functional germ cells. The same 
alternative explanations that were offered for the Begonia case apply 
equally well here. Numerous other cases of the same sort are well 
known to all zodlogists. To the advocate of the “ germ-plasm” theory 
