Plant Sanitation, 



433 



[November, 1909. 



destroy all the abortive sprouts as soon 

 as it is ascertained that they have 

 ceased growing. As the normal growth 

 of these giant sprouts is extraordinarily 

 rapid — sometimes reaching as much as 

 twelve inches within the twenty-four 

 hours — the stoppage of growth is uot 

 difficult to determine. The diseased 

 sprouts should be cut off level with the 

 ground and buried deeply in the soil. 

 They are so full of sap that it would 

 be impossible to burn them. 



The large hairy caterpillars of the 

 moth ( Taragama dorsalis ) have been 

 defoliating 'Dadap' (Erythrina) trees 

 growing amongst the Hevea on a rub- 

 ber plantation. It was suggested that — 

 after exhausting the supply of food to 

 be found on the Dadap — they might 

 turn their attention to the rubber trees. 

 To test this point, I deprived some of 

 the caterpillars of their accustomed 

 food and supplied them with Hevea 

 leaves alone. They did not appear to 

 be dissatisfied with the change, but fed 



freely and eventually completed their 

 transformations. This species must 

 accordingly be looked upon as a potential 

 pest of Hevea rubber, though it has not 

 yet been found actually feeding on rub- 

 ber in the field. The caterpiller is a 

 large and fairly conspicuous one. It 

 very closely resembles its still larger 

 ally Suana concolor, and should be 

 handled with equal caution. (See note 

 on page 136 of the August number). 



Mahogany trees, at Kandy, have been 

 partially defoliated by the caterpillars 

 of the 'Green Lappet-Moth' (Trabala 

 vishnu.) 



Cucumber roots, badly infested by 

 the ' Root Gall- worm ' (Heterodera radi- 

 cicola) have been received from the 

 Superintendent of School Gardens. The 

 treatment for this pest consists in a heavy 

 dressing of lime, after which the land 

 should be left fallow, or planted with 

 some crop that does not harbour the 

 worm. 



SCIENTIFIC AGRICULTURE, 



ACIDITY IN SOILS. 



(From the Gardeners' Chronicle, No. 

 1,174, Vol. XLV., June 26, 1909.) 



Important as are the nitrogen-fixing 

 bacteria, they form only a small part 

 of the microflora of the soil; other 

 groups of organisms prepare the food of 

 plants ; some break down the nitro- 

 genous compounds constituting manure 

 or humus into simpler nitrogen com- 

 pounds and finally oxidise them into 

 the nitrates, in which form most plants 

 obtain the nitrogen they require. Other 

 bacteria are, from the point of view of 

 the horticulturist, wasteful in that they 

 convert the nitrogen compounds into 

 free nitrogen ; others, again (particu- 

 larly certain microfungi), compete with 

 the crop for the plant food in the soil, 

 and perhaps produce substances which 

 are injurious to plant life. The relative 

 predominance of particular groups of 

 organisms, useful or injurious, can be 

 effected by the farmer or gardener, 

 because the various species of micro- 

 organisms are very sensitive to minute 

 changes in the soil, for example, its 

 acidity or alkalinity. 



Soils that are distinctly acid in their 

 reaction are not infrequently met with 

 in nature ; when they are in grass they 

 may be recognised by the generally 



rusty aspect of the vegetation, which 

 consists mainly of shallow-rooting 

 grasses growing in tufts, and by the 

 absence of Clover ; when they are under 

 arable cultivation their acidity may be 

 revealed by the presence of such weeds 

 as Spurrey, Sheep's Sorrel, and Corn 

 Marigold, and by the "clubbing" of 

 cruciferous crops. 



Similar acid soils have been produced 

 artificially by the long-continued use of 

 sulphate of ammonia as a fertiliser. The 

 best example is afforded by the con- 

 tinuous Wheat and Barley plots on the 

 farm of the Royal Agricultural Society at 

 Woburn ; where ammonium salts have 

 been used as the source of nitrogen the 

 land is now almost sterile, Barley 

 refuses to grow at all, and the whole 

 plot becomes covered by a growth of 

 Spurrey. At Rothamsted, where the 

 arable land is sufficiently furnished with 

 carbonate of lime, acidity has not set in, 

 but on the grass plots it has become 

 very marked. 



In order to determine the cause of this 

 acidity experiments have been made tc 

 see if any purely chemical or physical 

 interactions would take place between 

 the constituents of the soil and solutions 

 of ammonium salts, which would split 

 off a free acid from the latter, but with 

 negative results. The action was found 



