370 



THE AGRICULTURAL NEWS. 



Novembeb 20, 1915. 



nitrogen in this way finding an entrance into the 

 roots of plants in a less concentrated form than 

 ammonium nitrate. 



ninal ion of caca in I >ominica it 



was found 3 thatal the end of several years' trials, the 



amounl of nitrogen was greater than al the outset, and 



this is attributed to nitrification. A bacterial 



different soils clearly demonstrated the 



n fixing organisms, and il has been 



ocludi 'I that under the condil ions of the plot 



ixperiments referred to, considerabl 6ions of 



rogen ma} occur as the result of the action of free 



nitrogen-fixing bacteria of the Azotohacter type, and 



thai the amounl of nitrogen fixed max be very 



41. 'ail d iii the presence of an ample supply 



of organic matter. 



These conclusions are very important because 

 nitrogi □ fixation is not supposed to play an act ive part 

 in such soils, at any rate under temperate conditions. 

 An interesting nbte J has appeared on nitrogen fix- 

 ation in Danish forest soils. Azotohacter chroococcum 

 is 1111K occasionally present in these soils but. in some 

 localities where there is much calcium carbonate, two 

 1 In r species of Azotohacter were found present. The 



ises of the abseni f the principal species from 



forest soils were thought to be due to lark of 

 ■iiiin carbonate, to too lov> a temperature, and to an 

 -excess of humic matter. 



That temperature is an important factor has bei n 



ii reeenl h in [ndia '. and it may explain the 



apparent divergence between the cases of Azotohacter 



and the orchard and forest soils of Dominica ami 



Denmark. In general, 30"C. was found to be the 



ipti in temperature for maximum activitj in India, 



and it would appear therefore that warmth is an 

 important factor. 



In the Dominica investigations the temperature 

 ..1 the plots was studied, and tin- observations never 

 eading higher 1 han 2."> < '. 



Ii h be remembered that ohough they have 



many features in common, the conditions of an orchard 

 soil and a forest soil are not absolutely parallel. s " 



tin- n< 1 1 11 li il annual n hi of true forest -nils has been 



1 Watts, West Tndian Bn tetin, Vol. XIV, No. 2, p. L05. 



- Russell, E. •!.. .s . 1 ! Growth. 



Ti nipany, II'..,/ I Vol, XIV, No. l', p. 88. 



1 Reprod I in 1 he 1 '. Vol. \ I TV, 



No. 2. 



"■ Walton, .1. 1 1 , t/< m -- n\ 0) Igi Mure 



in India (Bacteriological Series) Vol. I, No. 1. 



111 tide in the Wt - [ndies, and we do not know whether 

 Azotohacter occurs in th.-m or not. It' these nitrogen- 

 fixing organisms are absent, it would be interesting to 

 know how the supply of nitrogi n is maintained. The sug- 

 tion arises as to whether mycorhiza may not play an 



important part. The fungi of 11 1 live either r 



m the roots ofp rowing in humus soils, and are 



verj « idely distributed. The relation between the fun| 

 and root is generally syn ! 1- to say, useful 



to both organisms, at least in the case of those which 

 live within the root 8 , the fungus assisting in 

 collection of nitrogen and in the elaboration of 

 albuminoid substances in return for carbohydrates 

 manufactured bj fchegreen plant. There are instances 

 where the union occurs between a fungus and 

 a non-chlorophyllous plant, as in the case ui Neottia. 

 Here we apparently have an example of a higher 

 plant parasitic on a fungus, and it is difficult to see 

 what advantage is derived bj the fungus. In general 

 it is more than likely that fungi oi mycorhiza arc of 

 greatest value to the higher plants on account of their 

 capacity for manufacturing higher nitrogen 

 compounds from soluble humus which they absorb from 

 the soil 7 , [t should be pointed oul as an interesting 

 morphological feature of the roots of trees bearing the 

 externa] fungi, that rool hairs are entirely absent, 

 a circumstance which shows that the fungus 

 functions as an organ of absorption. 



The extent te which mycorhiza plays an act 

 part in 1 he nut 1 il ion of 1 ropical forest plants is 

 definitely known, and it would be interesting if > I lis? 

 question were given specific attention in the West 

 Indies. Further, it ma} be the subject oi enquiry 

 whether many of our 1 conomic plants like rubber and 

 cacao can, under certain soil conditions, make use of 

 mycorhiza, especially where the soil is typically acid. 



It would appear desirable for the planter to 



realize that the presem f li , the importance of 



which in the sell has been so strongly emphasized, dues 

 not seem always necessar} for orchard or forest fertility. 

 Acidity does not appear injurious, and max even 

 be beneficial, as is thought to be the case with rubber 

 in the Federated Malay States 8 . 01 course with arable 

 soils, effects other ;than neu ion have to be consid- 



i Here lime is important because of its physical 

 as well as its chemical properties, rendering the soil 



■ Schimper's Plant Gfi ograph 1/, p. L09. 



■ Jost's Plant Physiology, p. 241. 



It wi tiff, M . 1 .■ dlttin, F.M.S., Vol. Ill, 



No. •-'. 



" Pangaiiiban, E. A.. The Philippine Agrieultiuisl 

 Fortster, Vol. IV. No. 4. (July 1915.) 



