950 



SCIENCE. 



[N. S. Vol. XXI. No. 547. 



Hydrodictyon and Vaucheria) ; several 

 fungi (Spowdinia grandis and Saprolegnia 

 mixta especially) ; certain yeasts and bac- 

 teria, and finally, to several species of 

 phanerogams. While with the algag the 

 light relation is of prevailing importance, 

 with the fungi it is more particularly a 

 matter of nutrition or transpiration. As a 

 rule, with the latter Klebs finds the stim- 

 ulus to reproduction in the failure of the 

 food supply in the immediate vicinity of 

 growth. That is, beginning with a well 

 nourished 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 phan- 

 erogams it Avould 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 

 groAvth in a flowering axis. It is probable 

 that all shades of difference will be found 

 in the capability of plants to have these 

 processes distinguished by releasing stim- 

 uli ; and it remains for the future to de- 

 termine to what extent this is possible. 



The general law which seems to be war- 

 ranted is, that conditions most favorable 

 for growth do not favor reproduction. The 

 problem then is to determine for every or- 

 ganism what ai'e these conditions under 

 which, on the one side, growth, and on the 

 other, reproduction, may occur. AA^hether, 

 under any circumstances the complete 

 cycle of development may be run Avithout 

 any change in conditions apparently 

 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 char- 



acters as may be due to the presence of 

 diffusible metabolic products, or products 

 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 de- 

 gree, but here the real problem is to de- 

 termine what constitutes hardiness. 



Fusion possibilities in vegetative cells 

 are more or less common in all groups of 

 plants. In basidiomycetes parallel fila- 

 ments fuse under many conditions of 

 development, and a pseudoparenchymatous 

 tissue may result. In grafting, the layers 

 which fuse may represent different spe- 

 cies 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 spe- 

 cies of myxomycetes (at least when pro- 

 duced 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 dissi- 

 pated by diversity of conditions under 

 which the plants may be grown. The solu- 

 tion of such problems with simple and 

 rapidly culturable organisms may even 

 throw some light upon the more complex 

 problems of self sterility and prepotence 

 (in the sense in which these terms are used 

 horticulturally) in higher plants— phe- 

 nomena which may not be explained with 

 present information. It has been found 

 that tomato and tobacco fruits are some- 

 times formed without pollination ; and the 

 same is true of other. plants. In certain 

 cucurbits the act of pollination seems to 

 afford a stimulus for the development of 



