274 



THE AGRICULTDRAL NEWS 



August 31, 191 2. 



than those that dissolve easily: 'so that, speakii)g 

 generally, it may be said that the substances which 

 penetrate most readily into the leaf tissues and pro- 

 duce effects such as have been described are those 

 which are least readily soluble in water.' 



What has been said makes it evident that the 

 prussic acid and the oil of bitter almonds do noc 

 exist in the leaf until the influences mentioned have 

 been brought to bear. The actual process is that a sub- 

 stance (prunasin) belonging to the class of bodies called 

 glucosides is caused to break up and, with the aid of 

 water, to form those compounds, together with the sugar 

 glucose. This decomposition is brought about by the 

 action of an enzyme, or unorganized ferment, in the cell 

 sap, which is probably, under ordinary conditions, 

 separated from the glucoside by a inenibrane through 

 which it cannot pass. The 'stimulus' for the decom- 

 position caused by the substances mentioned \vould 

 then consist in their power to enable the enzyme to pass 

 through the membrane. 



Other interesting observations connected with the 

 matter have been the outcome of experimentation, but 

 it will be sufficient here to allude to the work of 

 Professor H. E. Armstrong and Dr. E. F. Armstrong, his 

 son, which has shown that plants are provided with 

 membranes which allow certain substances, including 

 water, to pass, but are not permeable by other sub- 

 stances; it is because of the possession in their cells of 

 such membranes that leaves do not lose any of their 

 contents even when they are w-ashed b\- the heaviest 

 rains. It has been proposed to apply the term Hormone 

 to all substances that can penetrate those membranes, 

 or differential septa as they are called, and further, 

 the theory has been put forth that such substances 

 exercise their disturbing influence, in the cells into 

 which they have penetrated, by permitting the enzymes 

 already present to become active. 



The affair derives its practical importance from 

 the power of plants to employ, as food, compounds that 

 they have already built up in their cells. It seems 

 that stimulation is required for this, in order that the 

 enzymes may be brought into action and cause the 

 production of substances that are carried to other 

 parts of the plant, where they are wanted for growth. 

 In nature, it appears that ammonia is the most active 

 stimulant, while carbon dioxide also acts as a hormone. 



The matter to which all this consideration has led 

 is the question whether the soil, or manures, contains 

 substances which may bring about such actions in the 



roots of plants. It is well known that, while amnioni- 

 acal manures, including pen manure, form some of the 

 best manures when they are employed carefully, their 

 use in large quantities or in a concentrated form, as 

 for horlicuUural purposes, may actually kill the plants 

 that they are intended to benefit. This is quae in 

 accordance with what should be the effect of ammonia 

 if it acts as a hormone, for the stimulating action of 

 these bodies is only exerted when they are present in 

 an amouDt below a low maximum — above this max- 

 imum they are poisonous. Further, an explanation is 

 indicated of one of the reasons for using well-rotted 

 pen manure in preference to the fresh dung: in the 

 latter, the early changes due to putrefaction cause the 

 ammonia tn be liberated so quickly that it is harmful. 



Some explanation of the beneficial effects on plant 

 growth by the partial sterilization of the soil* has been 

 sought in the supposition that the process results in 

 the production of hormones such as ammonia which 

 subsequently exert their stimulating action on the 

 plants raised in the soil: a similar explanation is adduced 

 for the better germination shown by seeds sown in 

 partly sterilized soil. In either case, if the soil is 

 sterilized by heating it very strongly, growth is made 

 slower, and germination retarded,^ at first, suggest- 

 ing that the hormones are present in poisonous propor- 

 tions after the treatment, and that these proportions 

 decrease gradually to those in which the action is 

 stimulating. 



These matters serve as an addition to the many 

 illustrations of the fact that the investigation of the 

 relationships between the soil and the plant is of much 

 complexity. The continuation of the work in connexion 

 with them will doubtless give results of practical value 

 in enabling the agriculturist to know more accurately 

 how he may give the plants in which he is interested 

 the conditions that will lead to their most economical 

 productivity. 



DEPARTMENT NEWS. 



The Imperial Commissioner uf Agriculture re- 

 turned to Barbados, from Dominica, by the S.S. 'Oruro' 

 on August 22, 1912. It is expected that Dr. Watts 

 will leave Barbados on August 30, by the S.S. 'Oruro', 

 for the purpose of making an official visit to St. Vincent, 

 and that he will return to Barbados by the S.S. 'Ocam«' 

 0!. .September 14. 



*A(/ricuUuralJfews, Vol. IX, pp. 17 and 33. 



'"AgrkuUnral Neu's, Vol. YIIT, p. 281. 



