26 



yet tried. In pot experiments unrotted straw greatly increased 

 the numbers of nodules formed on each plant; there was, how- 

 ever, no increase of yield till phosphates were added. A dressing 

 of straw and phosphate has been found in field tests to be an 

 elfective fertiliser for beans and affords a method of increasing 

 the organic matter of the soil which might find useful application 

 in practice. 



The second investigation brings out the fact that the plant 

 is just as important as the organism in the partnership. It arose 

 as a result of Miss VVarington's important discovery that many 

 leguminous plants fail to grow unless supplied with traces of 

 boron. Dr. Brenchley and Mr. Thornton, taking the broad bean 

 as their example, showed boron to be essential to the proper 

 functioning of nodules on its roots. In the normal course, 

 conducting vessels grow out from the vascular system of the 

 plant root and enter the nodule. Along these vessels food 

 materials are brought from the plant to the bacteria, and the 

 products of their activity are carried back to the plant. The 

 vessels thus act as conduit pipes, connecting the organisms with 

 the plant and making the partnership effective. In the absence 

 of boron these vessels do not form or are very weakly developed. 

 The organisms, losing their normal source of food, become para- 

 sitic and destroy the plant protoplasm, being then harmful instead 

 of useful to the plant. The work thus shows that the organism 

 is a potential parasite; only by the nice adjustment occurring 

 in the healthy plant can the beneficial partnership be maintained. 



In most soils there is apparently sufficient boron to allow 

 of full development. But instances are on record in Japan, and 

 possibly elsewhere, where peas, which do not need boron, will 

 grow while other leguminous plants which need it will not. In 

 these soils there might be a boron deficiency. The more important 

 result emerges that the successful growth of a leguminous crop 

 depends on three conditions : presence of the proper organisms 

 and soil conditions necessary for their growth ; the proper nutri- 

 tion of the plant; and development of the conducting system 

 linking the organisms in the nodule with the circulating system 

 of the plant. 



Liming. 



The effect of lime on sour arable land and on certain kinds 

 of grass land is well known and farmers are frequently advised 

 to use more of this substance. But directly they begin to follow 

 the advice they are faced with the difficulty that analysts cannot 

 as a rule inform them just how much lime per acre they should 

 apply, and a round figure of one or two tons per acre is often 

 suggested. The recommendation suffers from the defect that no 

 farmer can afford to supply two tons per acre if one ton is suffi- 

 cient, apart from the consideration that too large a dressing may 

 injure the. crop or the soil. 



Various empirical methods have been devised from time to 

 time to givt some idea of the quantities needed, but the different 

 tests gwt different results, and in absence of definite knowledge 



