140 PLANT PHYSIOLOGY 



problems relating to the internal mechanism of response and to the 

 exact methods of transmission of the stimulus, as well as to the 

 immediate changes in the cells affected. 



A word may be said concerning the regeneration phenomena, 

 which are strikingly characteristic of the lower groups of plants, 

 but which in the higher plants do not seem to be well emphasized, 

 and are certainly less understood. The regeneration of the root-tip has 

 been best studied. In none of the higher plants has it been possible 

 from a single isolated active non-sexual cell, or a small group of 

 cells, to regenerate the plant. 



Although a study of the physiology of reproduction may be said 

 to have had its origin in the early observations of Camerarius, all 

 early studies represented largely only the ecological aspect of the 

 subject. It is only in very recent years that rapid strides have been 

 made in the general physiology of reproduction. The effect of con- 

 ditions upon the production of antheridial or archegonial thalli, 

 or of pistillate or staminate flowers among dioecious and polygamous 

 plants, has received very slight attention. During the present year 

 Laurent has published the results of experimentation during a period 

 of seven years with the effects of fertilizers, or plant nutrients, 

 upon spinach, hemp, and Mercurialias annua. It will be seen that 

 according to his results an excess of nitrogen or calcium has a tend- 

 ency to produce staminate flowers in the spinach, while potassium 

 or phosphorus tends to increase the production of pistillate flowers. 

 The seed produced on the pistillate flowers of these plants gave a 

 preponderance of female plants; but from these plants, in turn, 

 the seed yielded a larger number of staminate plants. So far as I 

 have been able to learn, it has never been determined if in a case of 

 dicecious perennial plants it is possible by a change of conditions to 

 induce a temporary or permanent change from pistillate to stamin- 

 ate flowers, or vice versa. In the same way, the influence of graft- 

 ing or budding a scion of one upon the other has not been made out, 

 although it is assumed that the flower will be characteristic of the 

 scion. 



It is with reference to the effects of external conditions upon the 

 production of sexual and asexual fruiting organs that unusual 

 progress has been made. In this direction a field of great magnitude 

 has been opened by the work of Klebs, and it is evidently being 

 pursued along all possible lines. As yet this work has been extended 

 only to a few green algae (as, for example, Hydrodictyon and Vau- 

 cheria); several fungi (Sporodinia grandis and Saprolegnia mixta 

 especially) ; certain yeasts and bacteria, and finally, to several spe- 

 cies of phanerogams. While with the algae the light relation is of pre- 

 vailing importance, with the fungi it is more particularly a matter 

 of nutrition or transpiration. As a rule, with the latter Klebs finds 



