10 



nitrogen-starved barley plots an increased crop was obtained, similar 

 to that which a dressing of nitrogenous manure would have given. 

 This result, however, only followed when the sugar was added 

 in the warm autumn weather ; in cold spring the sugar had a delete- 

 rious effect. 



Dr. Winifred E. Brenchley has continued her plant work on the 

 same lines as before. The amount of growth a plant makes in a 

 given soil is known to depend on the amount of food supplied, and 

 this relationship forms the basis of the connection between the plant 

 nutrition work and the soil work. But a hypothesis is current, and 

 is backed by sufficient circumstantial evidence to make it worthy of 

 consideration, that inorganic plant poisons act as stimulants to growth 

 if supplied in sufficiently small quantities. If this hypothesis were 

 well founded it would introduce a wholly new set of factors into 

 plant nutrition relationships and would, in addition, form a basis for 

 important practical developments. Water cultures have, therefore, 

 been made to test this hypothesis as completely as possible. The 

 compounds tested have been copper sulphate, manganese sulphate, 

 zinc sulphate, sodium arsenite, arsenious acid and boric acid, and a 

 wide range of concentrations has been adopted. N umerous plants have 

 been tried, but on the whole barley and peas have proved most 

 satisfactory. Copper sulphate was invariably toxic, even in such 

 high dilutions as 1 part of the salt to 10 millions of water. The effect 

 varied, however, with the plant, and was considerably masked in 

 presence of nutrient salts. The fact that boric acid decidedly in- 

 creased the growth of peas raises the interesting question whether 

 boron is in some way advantageous to the pea and therefore to be 

 regarded as a nutrient. In the case of barley no similar increase 

 in growth has yet been obtained. Some specific effect is clearly 

 indicated and the hypothesis is shown not to hold in its general form. 



The w^eed investigations have been carried into Norfolk this 

 season. Although the w^ork is not yet concluded, certain general 

 conclusions are already beginning to take shape. A definite asso- 

 ciation seems to exist between the weeds and the soil, the determin- 

 ing factor being, however, the texture of the soil rather than its 

 geological origin, excepting only in the case of the chalk soils. 

 The association is sometimes so close that it extends over a wide 

 area ; thus Euphorbia exigua and Raiiiuiculus arveiisis were 

 always seen on heavy loams or clays. Sometimes, however, the 

 association is affected by climatic or other factors ; thus Matricaria 

 inodora was common on clay in Bedfordshire but absent near Bath. 

 The two cases are distinguished as "general" and "local" association. 

 Very few plants, however, could be said to be symptomatic of soil 

 conditions in the sense of being restricted to any one type of soil, 

 but a good many plants are characteristic, i.e., are more frequently 

 found associated with one soil than with any other. Rumex acefo- 

 sella, Spergida arveiisis and Sceleranthits ainiiius may be regarded 

 as symptomatic of soils giving no carbonate reaction with dilute 

 hydrochloric acid. A relationship also exists between the weeds 

 and the crop : various species of Geranium and Plant ago lanccolata 

 are very common in temporary grasses ("seeds" crops), while Poa 

 annua, Polygonujin aviculare and P. convolvulus are very rare. No 

 doubt the conditions of cultivation account for this. It is sur- 

 prising how many of the weeds belong to the Conipositcc, at least 



