SCIENCE 



[Vol. LV. No. 1410. 



the formative laws governing the organism a 

 dozen or more layers of cells surrounding the 

 embrj'o of the wheat or maize are completely 

 absorbed and in the end the innermost remain- 

 ing walls of the ovary are literally cemented 

 to the outer unabsorbed layer of the inner 

 integument.!'' Here is emphatic control of cell 

 walls by the life inhabiting them, control ex- 

 erted chiefly through the agencj' of the Ca-ion- 

 equilibria of the tissues concerned. Finally 

 this control in the wheat as in Herbst's sea 

 urchin embryos is shown by the fusing together 

 of outer surfaces of cell walls. Here we seem 

 to have clean cut instances to show how in the 

 formative processes the living material is able 

 to command the structure it forms about itself- 

 The outer walls of cells originally located far 

 from each other are brought together by the 

 solution of intervening structures. The sub- 

 stances necessary for the formation of the 

 cementing layer seem to be extruded from the 

 protoplasm thi'ough the wall to the outside 

 surfaces where they unite to form the coagulum 

 seen. Perhaps the Ca ions and the peetase 

 thrust through from the interior of the cell 

 meet at its frontier the pectin which under 

 enzyme action yields pectic acid in the pres- 

 ence of the Ca ions. The product of such an 

 occurrence would be seen in the cementing layer 

 formed on the outside of each of the now 

 neighboring cells. 



In conclusion, I should like to refer briefly 

 to some of the more practical results that 

 seem to flow from the considerations that have 

 been here set forth. 



It appears that a certain quantity of Ca ions 

 must be present in the medium for the main- 

 tenance of the chemical and functional integ- 

 rity of the cell wall, as well as the chemical 

 and functional integrity of the deeper lying 

 living parts of the cells of absorbing roots of 

 higher green plants. When this is so inain- 

 tained, absorption takes place in the manner 

 we are accustomed to call normal. When this 

 necessary minimal supply of Ca ions in the 

 medium is lacking, be it in soil solution, water 

 culture, or sand culture, the function of 

 absorption is upset and a more or less marked 



17 True, R. H., Bot Gaz., IS: 212-226. 1983. 



leaching of ions from the plant follows. In 

 the absence of this necessary minimum of Ca 

 ions, the soil solution or culture solution may 

 be rich in all other required ions, but these 

 are useless to the plant. They are unabsorb- 

 able. This brings us face to face with a con- 

 dition of affairs in plant nutrition that has 

 not been recognized and therefore has not been 

 characterized. We may fairly say that Ca 

 ions make physiologically available other 

 equally indispensable nutrient ions. The prac- 

 tical consequences that follow from this way 

 of looking at the fertilizer problem have not 

 thus far been realized. We learn why from 

 earliest times civilizations have grown up on 

 soils rich in limestone debris. We learn why 

 agriculture has readily succeeded in some 

 regions, not in others. We understand why,, 

 by tlie^use of lime, lands have been rendered 

 capable of supporting largely increased popu- 

 lations. We are now able to correlate these 

 broad facts with those of cell physiology and 

 to suggest perhaps not the calcium function 

 sought by Jost, but one way perhaps of many 

 in which higher green plants find calcium 

 necessary. 



Rodney H. True. 

 Botanical Laboeatort, 

 University of Pennsylvania. 



THE METHOD OF SCIENCE IN AGRI- 

 CULTUREi 



To be practical has been the great goal of 

 agricultural investigation from the beginning. 

 It was entered upon with a practical purpose, 

 and in a large degree practical results early 

 came to the expectation of the farming people. 

 Here was a type of science which was not 

 working in the clouds for its own sake, but 

 down in the dirt where the problems of farm- 

 ing lay. 



It is fortunate that this has been so — that 

 this close sympathy and this urge to meet the 

 needs of the art have been felt so keenly. It 

 has given life as well as purpose to our branch 

 of science, and the wide extent to which its 



1 Address of the Vice-president and Chairman 

 of Section O — Agriculture, American Association 

 for the Advancement of Science, Toronto, 1921. 



