VENATION AND SENESCENCE OF POLYEMBRYONIC CITRUS PLANTS 327 
develops first and much more rapidly than the one arising from the fertilized 
egg; that in some cases the former, wholly or partially, suppresses the 
development of the latter. Osaw'a (1912) states that it is very common for 
as many as nine embryos to be present in the embryo sac, yet only rarely 
do more than four develop. 
These observations all tend to show that the relative size and vigor of 
polyembryonic plants is primarily a matter of priority of development and 
food content of the cotyledons. The embryo, whether gametic or apogam- 
ous, which has the initial start and the greater reserve of food will probably 
produce the larger plant. In those cases in which the embryos develop 
simultaneously, we should expect to have plants of equal size and vigor. 
Discussion of Results 
The important question, of course, is this: Do the results have any 
bearing upon the question of rejuvenescence in plants? 
Rejuvenescence in the sense in which Minot (1908), Child (1915), and 
Conklin (19 13) define the term will be used here. They hold that reju- 
venescence is a condition of an organism indicated by metabolic activity 
increased over what it was prior to the change; and that the methods by 
which such an increased rate may be indicated vary, but the process is 
always the same — a partial or entire undifferentiation," or unloading of 
differentiated products which interfere with maximum metabolism. In a 
general way it may be said that differentiation and growth are gradual 
processes, usually having their origin in a single cell. This passage from 
the simple to the complex in the life cycle of an organism is invariably 
accompanied by a gradual retardation of the rate of metabolic activity, 
which finally ceases, and death ensues. Minot aptly says that death is 
the price paid for differentiation. On the other hand, the process of 
" undifferentiation " must and undoubtedly does take place. Just what the 
process is, and how it may be effected, is still largely a matter of conjecture. 
It has been quite generally assumed that sexuality is essential to re- 
juvenation. Child has shown that complex organisms may be partially 
rejuvenated by a period of partial starvation, and Conk^'n calls attention 
to the rejuvenation which apparently takes place in frogs and other animals 
after a period of hibernation, comparable to the starvation period of Child. 
He also suggests that such periods of rest and encystment shown by many 
animals and plants are directly correlated with partial rejuvenation proc- 
esses. Furthermore, Child has shown that apogamous reproduction is 
just as effective as gametic reproduction in securing rejuvenescence. In- 
deed, this would seem to be the case in plants like the banana whose sexual 
apparatus for unknown periods of time has been inoperative, and yet in 
which there has been no indication of the plant's "running out." 
Now all the evidence gathered in the study of polyembryonic Citrus 
