PLANT PHYSIOLOGY PRESENT PROBLEMS 141 



the stimulus to reproduction in the failure of the food-supply in the 

 immediate vicinity of growth. That is, beginning with a well-nour- 

 ished mycelium, a diminution of food-supply, other conditions being 

 constant, usually compels reproduction. A change in the specific 

 chemical content may be effective, and in other cases there are other 

 concurrent stimuli. In the study of phanerogams it would seem 

 that the problem is one which is, as a rule, far more complex. It has, 

 however, been found possible with a few species to produce at will 

 continuous vegetative growth or continuous flowering, to induce 

 fruiting in a well-nourished vegetative shoot, and to incite vegetative 

 growth in a flowering axis. It is probable that all shades of differ- 

 ence will be found in the capability of plants to have these processes 

 distinguished by releasing stimuli; and it remains for the future to 

 determine to what extent this is possible. 



The general law which seems to be warranted is, that conditions 

 most favorable for growth do not favor reproduction. The problem, 

 then, is to determine for every organism what are these conditions 

 under which, on the one side, growth, and on the other, reproduction, 

 m&y occur. Whether, under any circumstances, the complete cycle 

 of development may be run without any change in conditions ap- 

 parently awaits proof. 



In grafting it would seem that seldom, if ever, do any characters 

 of the stock pass into those of the scion except such characters as 

 may be due to the presence of diffusible metabolic products, or pro- 

 ducts capable of self-propagation upon requisite stimulation. In 

 this manner it has been shown that albinism may be transmitted 

 from stock to scion. Again, Strasburger has indicated that atropin 

 is accumulated in the potato when on a potato stock there is grafted 

 a scion of Datura stramonium. It has been found that hardiness 

 in the stock may affect the scion to a marked degree, but here the 

 real problem is to determine what constitutes hardiness. 



Fusion possibilities in vegetative cells are more or less common 

 in all groups of plants. In basidiomycetes parallel filaments fuse 

 under many conditions of development, and a pseudoparenchy- 

 matous tissue may result. In grafting, the layers which fuse may 

 represent different species or even different genera. Little is known 

 concerning the factors influencing such fusions. Allusion may also 

 be made to the fact that plasmodia of the same species of myxomy- 

 cetes (at least, when produced in nearly similar conditions) fuse 

 with one another. It should be accurately determined if this is an 

 inherent property of the same race or species only, and if this fusion 

 tendency may be weakened or dissipated by diversity of conditions 

 under which the plants may be grown. The solution of such pro- 

 blems with simple and rapidly culturable organisms may even throw 

 some light upon the more complex problems of self-sterility and 



