STRUCTURE AND HISTORY OF PLAV, 253 
considerable amount of material was available for the beech, it was far from 
sufficient. 
Apparently no plant can be defined by mass as it stands, not even the 
annual, because an annual can be converted into a perennial through changes 
that affect its nutrition (see р. 249). The annual apparently belongs to a type 
of plant which owing to peculiarities of nutrition does not normally develop 
its mass even approximately. Trees such as the willow, which are readily 
multiplied by cuttings—and according to my conception this is not repro- 
duction by artificial means—are also possibly unable to develop their mass 
in one whole even under the most favourable circumstances, but must be 
separated into parts to do so. The difficulties of the calculation of mass 
as regards the higher animals would seem to be even greater. Plants which 
are not multiplied by cuttings, the Coniferz for example, would probably 
most readily lend themselves to investigation involving measurements of the 
major unit or soma. In any case, the investigation of the major unit is 
obviously of vast, it might almost be said of insuperable, difficulty : nothing 
less than the preparation of exhaustive monographs of a very different order 
from those so far undertaken will suffice. 
The major individual, as already stated, I conceive to be a constant, and 
of prime importance. The circumstances under which a plant grows will 
not therefore, according to my hypothesis, essentially affect its final mass, 
provided of course that there is no actual crippling: whether the plant 
grow slowly or rapidly is in fact unimportant, for in either case the yield by 
mass of somatically produced material will be approximately the same. The 
vital energy of plants is in a static or in a kinetic state according to circum- 
stances. Thus in some environments growth will be so slow as hardly to be 
perceptible, and the vital energy will therefore toa large extent remain stored, 
as follows from the fact that buds as well as seeds have the power of remaining 
latent for a time, and therefore many more years elapse in the development 
of the major unit than in an environment where growth is rapid, that is to 
say, where the vital energy of the plant is in the kinetie state (see pp. 269 
& 270). In other words, the time factor is not fundamental as regards the 
development of the vegetal mass—the length of life of a plant major unit 
varles within very wide limits. The plant in fact has an age which can be 
reckoned in years, and also a biological age which I will call the absolute age. 
measured by the period, stage, ог position which it has reached in its life- 
cycle (see footnote on p. 267). 
The introduction of these questions in connection with the reed arose from 
the consideration of the significance of the great divergence in size of the 
reed-shoots forming different Plavs and different portions of the same Plav 
(see pp. 268-268), and from the conclusion that the large shoots were more 
youthful than the small ones, and that the plant finally ceases to produce 
even small shoots—that the major unit, in fact, dies owing to senescence. 
