PLANT PHYSIOLOGY PRESENT PROBLEMS 133 



that nothing whatever is known concerning the method by which 

 carbon dioxide is chemo-synthetically utilized by the nitrite and 

 nitrate bacteria. 



There are many interesting problems afforded by the general 

 phenomena of metabolism, with relation both to those products 

 which may be immediately utilized and to those which may be stored 

 up for future use. It is well known that during active growth special 

 foods may be taken out of circulation and stored up. The stimulus 

 to such storage is not easily determined. In many instances it is 

 apparently the protoplasm which is decomposed in order that these 

 storage products may be formed; therefore, so far as possible a 

 study of all protoplasmic decomposition phenomena is especially 

 necessary. The deposition of the cell-plate and the storage of reserve 

 cellulose are especially interesting. It will be extremely difficult to 

 follow the succession of changes involved, yet some information will 

 undoubted!} 7 be gained. 



The migration of compounds, particularly of those containing 

 nitrogen, magnesium, and potash, to growing vegetative parts and 

 to the developing seed is most remarkable. The production, whether 

 regulatory or otherwise, of the numerous by-products in the cell, 

 such as tannin, pigments, organic acids, etc., is also of peculiar inter- 

 est. The functions of some of these compounds must be most im- 

 portant, and should receive further attention. Tannin, particularly, 

 is doubtless of much economic importance in the regulation of turgor 

 and in augmenting the resistance to injurious external agents. Astruc 

 has recently shown that acids are found in the younger parts of non- 

 succulents and mostly in the region of maximum turgescence; and 

 that there is a progressive decrease of such compounds in the older 

 organs. In succulents, moreover, very slight changes in the external 

 conditions materially affect the acid content. 



It cannot be expected that all of the information desirable with 

 relation to the composition and action of hydrolyzing and oxidizing 

 enzymes will be obtainable until more is known of the proteids, to 

 which group the ferments seem to belong, or with which they are 

 at least closely related. Whether these enzymes are concerned with 

 the metamorphoses involved in rendering soluble or transforming 

 pectin, proteids, glucosides, starches, cellulose, fats, or sugars, their 

 physiological activities are in the highest degree remarkable, and 

 worthy of the closest study. The problems which relate to their 

 occurrence, composition, production, and action require, however, 

 the combined attention of physiologists and organic and physical 

 chemists. In recent times, through the work of Brown and Morris, 

 Fischer, Green, Prescott, Vines, Loew, Beijerinck, Newcombe, 

 Woods, and many others, these compounds have received renewed 

 attention. It may be that at present too many obscure phenomena 



