[Vol. 2 



256 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



ceilings, rafters, and plumbing, but the materials used may be 

 bricks, stones, metals, sand, lime, boards, glass, and paint. 

 Our present needs lead us to experiments with these com- 

 ponents rather than to trials of the possible combinations and 

 inhibitions, possibilities and impossibilities of sets of builders ' 

 blocks, no matter how complete or full these may be. 



Living material is a colloidal complex with its enmeshed re- 

 actions highly fluctuant, its combinations unstable and its 

 types of energy transformation multifold. It is concrete, 

 however, and amenable to experimentation of many kinds. 

 Its physical qualities and form undergo changes of phase 

 which have some correspondence with the mechanism of mor- 

 phogeny, reproduction, and heredity. Thus, for instance, in the 

 higher plants the germinal protoplasm in the earlier stages of 

 the individual is in the form of meristematic tracts made up 

 of highly distended plasts in which absorption of water, hydra- 

 tation, auxetic enlargement, and division of the separate ele- 

 ments is very marked and rapid. Elements at the peripheries 

 of these masses are separated which undergo differentiation 

 and pass into the permanent tissues of the individual. These 

 separating cells may be modified to an enormous extent by 

 external agencies; thus conditions of aridity acting upon an 

 individual may cause the tissues formed from its embryonic 

 tracts to make such structures as to give the organs which 

 they make up a xerophytic aspect. 



This final xerophytic or other character of the soma, how- 

 ever, is in the permanent tissue, and the modifications which 

 have resulted in its specialization ensued after the cells were 

 pushed away from the meristem, and there seems to be no 

 reflection of the final fixed qualities back to the embryonic 

 tract, although there are many promising possibilities to 

 be considered. Of these none are more interesting than the 

 regenerative processes by which highly specialized cells 

 reassume embryonic activity and reproduce members or indi- 

 viduals vegetatively. Actual tests of the transmission and 

 permanence of the specializations under these conditions have 

 not yet been made with that exactitude which would allow any 

 serious conclusion to be formulated. At certain stages of the 



