June, 1909.] 



Plant Sanitation- 



than by the introduction of temperate 

 species. And in a country where the 

 climate varies so much in different dis- 

 tricts as in Ceylon, it may be possible in 

 this way to obtain species adapted for 

 each district. With regard to the plauts 

 at present recommended, a word of cau- 

 tion is necessary in the case of the sensi- 

 tive plant, Mimosa padica. This is cer- 

 tainly a nitrogen collector, but its thorns 

 render it unsuitable for use in any culti- 

 vation which must be worked by bare- 

 footed labour. In one Ceylon coconut 

 plantation where mimosa is fairly abun- 

 dant though the land is periodically 

 ploughed, the coolies have to wrap up 

 their feet in sacking when gathering tlie 

 nuts, and even then many nuts are 

 allowed to remain in the thicker tufts 

 of mimosa. On another well-known coco- 

 nut plantation, seed of mimosa was 

 sown at considerable expense some years 

 ago, but far more expense is now being 

 incurred in the almost ineffectual at- 

 tempt to eradicate it. In one case, it 

 is kept down, though not eradicated, by 

 a flock of groats. Mimosa padica is, of 

 course, an introduced weed in Ceylon, 

 and is said to have been brought here 

 before 1824. It has not yet spread to the 

 Batticaloa district, though it is gra- 

 dually working its way there ; in 1908 it 

 was found about haif a mile beyond 

 Mahaoya on the Batticaloa road. 



Seeing that so few facts of Hevea cul- 

 tivation have been definitely established, 

 it is no doubt becoming increasingly 

 difficult for the compilers of treatises 

 on this subject to include new ideas 

 which could alone afford justification 

 for the multiplication of books. Under 

 such circumstances, the tendency ap- 

 pears to be to advise anythiug, no 

 matter what, so long as it is new. The 

 rubber industry has already suffered 

 considerably from the promulgation of 

 ideas which only required brief con- 

 sideration, from a botanical standpoint, 

 to demonstrate their absurdity. The 

 latest recommendation is that root prun- 

 ing should be practised. As a matter 

 of fact, this has practically been recom- 

 mended before in connection witn 

 trench systems of manuring, though the 

 fact was not recognised. In the present 

 case the author supports his recom- 

 mendation by the statements that root 

 pruning is almost universally practised 

 in the orange groves of California, and 

 that he has applied the system to coffee 

 with advantage. Apparently he applied 

 it to coffee without understanding the 

 reason. It is well known that root 

 pruning produces a larger crop in the 

 case of fruit trees, and a striking ex- 

 ample of this is quoted in the Journal of 

 69 



the Royal Horticultural Society for 

 March. 1909 : a horizontal pear tree, 

 twelve years old, which had never borne 

 any fruit, was root-pruned on one side ; 

 two years later that side of the tree was 

 covered with fruit, but there was none 

 on the other. If Hevea brasiliensis is 

 grown for seed only, by all means try 

 root pruning, but if a good growth of 

 foliage, and consequently of the stem, is 

 desired, root pruning should be avoided 

 at all costs. Apart from this the danger 

 of the attacks of fungi and white ants 

 should be a sufficient deterrent to any- 

 one who has thought of adopting the 

 practice. The presumed destruction of 

 fungi and termites by the small amount 

 of disturbance of the soil recommended 

 by the author in question is quite ima- 

 ginary. 



The most glaring error in the now- 

 discarded '' full spiral " system of tapping 

 was the failure to recognise that in 

 order to ensure a healthy growth of the 

 tree the development of the roots must 

 keep pace with that of the stem, or 

 rather, that the stem canuot develop 

 properly without adequate root growth. 

 The food materials required by the roots 

 are elaborated in the leaves, and are 

 conveyed down the stem by channels 

 which lie outside the cambium. The 

 " full spiral," therefore, practically com- 

 pletely interrupted the supply of food 

 to the roots, and no food could reach 

 them until the bark was renewed. Un- 

 fortunately, though it was recognised 

 that the ''full spiral" was "too hard 

 on the tree," it is evident that the true 

 reason of this has not been appreciated. 

 It is necessary therefore to insist as 

 strongly as possible that on no system 

 of tapping should the tree be tapped 

 over more than half its circumference 

 at the same time. This gives the maxi- 

 mum tapping area permissible where 

 financial considerations necessitate the 

 tapping of trees of small girth ; it should 

 not exceed one quarter of the circum- 

 ference under normal circumstances. 



All ideas on the subject of tapping 

 have been dominated by the dictum 

 that the bark must be preserved at all 

 cost. It may be questioned whether this 

 view is not a remnant of the a priori 

 ideas of latex formation which flourished 

 in the "boom" period. Of course, it is 

 unnecessary, when tapping by the ordi- 

 nary systems, to remove more bark than 

 is required to reopen the ends of the 

 latex vessels, but is there any advantage 

 in a system which does not require the 

 removal of the bark at all? Consider 

 the ordinary process of tapping by cuts. 

 The cut opens the latex vessels, and 



