368 Morphogenetic Factors 



(Polster, 1938), floral initiation begins some time before the change 

 from low to high C/N ratio takes place. In various plants that have been 

 brought to flowering by other means, such as chemical or photoperiodic 

 stimulation, the increase in C/N is much less conspicuous than under 

 natural conditions. In many cases, also, there is no precise ratio that may 

 be counted upon to induce flowering. Both in carbohydrates and com- 

 pounds of nitrogen there are many different chemical forms, and it is a 

 matter of doubt whether the ratio should regard total, soluble, or easily 

 available carbohydrate, on the one hand, and total, protein, or soluble 

 nitrogen on the other. 



Despite these criticisms, the general concept that in the living plant 

 there is at any particular stage a balance between various chemical 

 constituents and that a shift in this balance is related to a change in the 

 activities of the plant is an important one. The organism tends to maintain 

 a homeostatic equilibrium among its various processes but this is not a 

 static condition, for the equilibrium changes progressively as the or- 

 ganism develops from one phase to the next. This is so complex that 

 the ratio between any two chemical substances will usually give only an 

 incomplete picture of it. A study of the C/N ratio, whether this be 

 cause or effect of the onset of the reproductive phase, will doubtless 

 continue to provide information about this major step in the life history 

 of the plant. 



Other Elements. Much of what is known about the morphogenetic 

 effects of the other essential elements comes from observation of changes 

 in development produced when each is deficient in amount. These changes 

 are usually differences from the normal amount of growth or are ab- 

 normalities of various sorts, "hunger signs" resulting from insufficient 

 nutrition. The literature of physiology and pathology is full of such in- 

 stances. Venning (1953) has described the developmental effects of 

 deficiencies in sulfur, calcium, nitrogen, potassium, phosphorus, and iron. 

 The effects of the various trace elements have been reviewed by several 

 workers, among them Brenchley (1947) and Wallace (1950). 



A few of the effects of various elements are of morphogenetic interest. 



Phosphorus is of much importance in physiology and genetics because 

 it is a constituent of the nucleic acids. Morphogenetically it is significant 

 in relation to mitosis. Phosphate promotes cell division in roots but has 

 little effect on cell elongation, whereas nitrate promotes elongation but 

 not division. 



Stanfield ( 1944 ) analyzed roots and tops of staminate and pistillate 

 plants of Lychnis dioica and found that the staminate had a higher per- 

 centage of phosphorus than the latter in both vegetative and early flower- 

 ing phases. 



Pierce ( 1937 ) observed that in violet plants grown in nutrient solu- 



