March 18, 1898.] 



SCIENCE. 



573 



is accented by the efforts made to explain 

 tlie formation of these substances in a spec- 

 ulative manner upon ecological grounds. 



So far as general metabolism is concerned 

 it is to be said that the physiologist locates 

 a substance here and there in the cell as a 

 product of general processes, but he is in- 

 capable of more than ill-defined theories as 

 to the course of chemical changes. It could 

 scarcely be otherwise with the structure of 

 the chief components of protoplasm un- 

 known. The meager facts and abundant 

 differences of opinion concerning the con- 

 tents of resin ducts, laticiferous tissue and 

 ' excreta ' in general may well lead us to 

 hesitate in declaring these subjects ' closed ' 

 and fixed. 



The ascent of sap is a problem which has 

 defied the combined efforts of the physicist 

 and the physiologist for more than a cen- 

 tury, and the results obtained by several of 

 the most reliable investigators in the last 

 decade have only annihilated previous 

 hypothesis. In such manner capillarity, 

 imbibition, the intermittent activity of pro- 

 toplasm, the Jaminian chain, the lifting 

 power of transpiration, variations in tension 

 of enclosed gas-bubbles, and recently the 

 tensile strength of a column of water, have 

 each in turn held the place of importance 

 only to give way to the inexorable logic of 

 fact. It is generally admitted that the im- 

 bibition method proposed by Sachs is the 

 only known method by which water could 

 actually attain the summit of a tall tree, 

 and that this method loould furnish only a 

 minute fraction of the amount necessary. 

 On the other hand, it is well known that the 

 current does not travel in the walls, but 

 in the lumina and pits of the tracheal 

 elements. We shall be compelled to return 

 to the living elements and begin the investi- 

 gation anew. 



Time does not suffice to relate the de- 

 tailed problems of growth yet unsolved, but 

 it is becoming more and more evident that 



molecular features of growth are hardly at 

 all determined, as well as the relation of 

 this process to correlative and environ- 

 mental forces. 



The consideration of the effect of physio- 

 logical factors, such as nutrition, light, etc., 

 upon development and stature promises re- 

 sults of sweeping importance to all branches 

 of biological science, if the few contribu- 

 tions which have appeared in this depart- 

 ment may be taken as an index. 



The nature of the irritability of plants, its 

 development from the primitive reactions 

 of protoplasm, the mechanism of reaction 

 and transmission of stimular resultants, and 

 the general irritable organization of the 

 vegetal organism are yet hardly touched 

 upon. In fact, so little understood is the 

 sensitiveness of plants that biologists in 

 general stand aghast at the daring of those 

 investigators who seek to reduce it to terms 

 comparable with those used in the descrip- 

 tion of animals. 



As a specific case of incompleteness it 

 may be mentioned that the path or conduct- 

 ing body for impulses in plants has not been 

 determined in any single instance, nor has 

 any cohesive theory as to a method of 

 transmission ever been propounded. One 

 may readily imagine the condition of ani- 

 mal-physiology if all information concern- 

 ing the nervous system were wiped out of 

 existence, and it would be known that the 

 arm was moved by changes in form of lumps 

 of tissue in that organ, which were set in 

 motion when stimuli were applied to some 

 distant organ with no apparent connection 

 with the muscle. 



The subject of reproduction has hitherto 

 necessarily been considered from a purely 

 morphological standpoint, although hun- 

 dreds of titles of contributions upon the 

 subject wrongly denote a physiological 

 treatment. The time seems ripe for the 

 physiologist to carry on researches upon the 

 activities concerned, and some few splendid 



