165 

 680.-HOW TO TELL WHAT FOOD PLANTS WANT. 



N No. 72, Vol. IV, Agricultural News, January 11. was a 

 shorl resume of a paper from German sources on the study 

 of the appearance of plants when they want certain consti- 

 tuents of plant food. 



NITROGEN. — When they want nitrogen the leaves are said to Lose 

 their normal green colour and take on a clear green or a yellowish 

 one, and to dry finally with a clear brownish yellow colour. 



Phosphoric Acid. — When phosphoric acid is deficient, the leaves 

 take on a deep clear green, almost blue green. With a greater 

 scarcity there appears on the leaves, first at the margin, and later on 

 the whole leaf dark spots, and the leaf dies with a dark brown to a 

 black green colour. 



Potash. — A scarcity of potash is said to be coincident with 

 spotted leaves, the spots appearing in the margin, and later becoming 

 distributed over the whole leaf, the stalk, mid-rib and veins retaining 

 their green colour The leaf also curves or curls, with its convex 

 side upwards, and finally dry up. 



Our Cacao planters might usefully make observations on these 

 points as they must be of considerable interest, and if they prove 

 reliable, will readily afford them means of determining the wants of 

 their Cacao fields in the way of manures. In fact, it is a short cut, 

 which, if successful, will in a great measure do away with the neces- 

 sity of analysis of the soil, ahvays at its best, an expensive and 

 tedious operation. 



Like all many propositions however : it is in no way a new idea ; as 

 it has been followed by cultivators for generations. Many an observing 

 cultivator of farm or garden crops can tell by sight without perhaps 

 being able to tell the why and the wherefore, or able to describe the 

 exact appearance of his plants ; what particular manure they recpaire 

 to further their growth. They apply what they believe to be 

 required, and if successful, they repeat it on the next occasion. 

 It is this very thing that Lille, the great French Agricultural 

 Chemist recommends the practical man to do, and it is as he says, a 

 practical method of analyzing the soil of the field, by means of the 

 plants it will grow. 



681-THB SHAPE OP PLANT STEMS. 



In the Agricultural News of January 14th, 1905, a short note 

 gives a summary of an article by Lord Avebury on the above subject. 



The main features' of the paper are very amply illustrated in 

 Tropical Countries in the form and shape of our Forests trees. 



Anyone walking round the Queen's Park, in Port-of-Spain, may 

 see the principle described by Lord Avebury as, existing in British 

 plants, amply illustrated in the forms of the stem and branches of 

 our largest trees. 



