June 23, 1905.] 



SCIENCE. 



949 



the protoplasm of this high temperature 

 must also be of consequence. The external 

 conditions of temperature of the effects 

 of a modification of conditions are more or 

 less readily determinable ; but it has not 

 been possible to follow the internal 

 changes which result. It may be noted 

 that the freezing point of a plant is lower 

 than that of the expressed sap ; yet of 

 course the freezing point is not necessarily 

 a valuable indicator of injury. The effects 

 of temperature upon reproduction will be 

 treated of later. 



The symbiotic relationship of fungus 

 and root to Mycorhiza offers a fine oppor- 

 tunity for careful investigation. The 

 studies which have already been made 

 serve only to put the reader in a state of 

 hopeless confusion. 



The universal phenomenon of irritability 

 as manifested by trophic phenomena has 

 been a fruitful field of investigation. The 

 general methods of irritable response have 

 been determined ; and the best work of 

 such investigators as Haberlandt, Noll, 

 Czapek, Newcombe, MacDougal and others 

 has more recently been directed to the 

 deeper 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 re- 

 generation 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 Camer- 

 arius, 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 conditions upon the production of an- 

 theridial or archegonial thalli or of pistil- 

 late or staminate flowers among dioecious 

 and polygamous plants has received very 

 slight attention. During the present year 

 Laurent has published the results of ex- 

 perimentation during a period of seven 

 years mth the effects of fertilizers, or 

 plant nutrients, upon spinach, hemp and 

 Merciirialias annua. It will be seen that 

 according to his results an excess of nitro- 

 gen or calcium has a tendency 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 detennined 

 if in a case of dioecious perennial plants it 

 is possible by a change of conditions to in- 

 duce a temporary or permanent change 

 from pistillate to staminate flowers, or vice 

 versa. In the same way, the influence of 

 grafting or budding a scion of one upon 

 the other has not been made out, although 

 it is assumed that the flower will be char- 

 acteristic of the scion. 



It is with reference to the effects of ex- 

 ternal 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 algjTR (as, for example, 



