Nov. 1906.] 



395 



Plant Sanitation, 



issued in 1903, I wrote as follows :— "I have repeatedly observed that a vigorous 

 condition of the plant results in an obliteration of the earlier perforations and a 

 tendency to choke out the insects that have more recently gained an entrance into 

 the branches. The mouth of the tunnel is invaded by an ingrowth from the 

 vigorous cambial tissues. New wood is then formed, covering up the old wound, 

 and the plant is able to carry on all its functions without interruption." 1 am still 

 prepared to fully endorse this statement. The accompanying figure represents an 

 actual section through a piece of a tea branch where such an ingrowth has occurred, 

 (a) shows the cortex or bark ; (6) the cambium ; (c) the woody tissue ; (d) section 



of Xyleborus tunnel ; (e) an 

 ingrowth from the cambial 

 tissue, blocking the en- 

 trance to the gallery. 

 Though burning the prim- 

 ings is undoubtedly the 

 most efficient method of 

 destroying the insects con- 

 tained therein, it has been 

 found in practice to have 

 the serious drawback of 

 depriving the soil of a vast 

 amount of nitrogenous 

 material that could be 

 returned to it in the form 

 of green manure. I con- 

 sider that the benefit derived by the plant from a proper burial of the green 

 prunings will far outweigh any injury that may arise from the escape of a few of 

 the insects. If there is much heavy wood with the prunings, this may be first 

 separated and burnt. Where the complete destruction of prunings by fire is 

 insisted upon, it will be found necessary to replace the material by its equivalent 

 in either green or artificial manures, at considerably enhanced cost. Failing this 

 the tea will undoubtedly go back, — losing stamina from its inability to withstand 

 the repeated attacks of the pest. This question of the problematical escape of 

 some of the insects from buried prunings is rendered negligible by the fact that 

 it is generally impossible to ensure the complete eradication of every insect from 

 the tea bush by anything short of collar pruning. I am strongly opposed to th e 

 excessive punishment of the bushes that is sometimes inflicted in the endeavour 

 to cut out every borer. Such an attempt is quite futile. The points of attack 

 being quite distinct and separate from one another, it is impossible to be sure that 

 the pest has been eradicated without cutting up every branch ; and even then there 

 may be (and frequently are) tunnels in the main stem itself. Again, — without close 

 examination by means of a lens— it is difficult to determine whether any particular 

 tunnel is tenanted by the insects or has been deserted by them. I would prune 

 an infested tea bush — equally with an unaffected one— according to its growth of 

 wood. The object in view is the production of strong sappy shoots, and if any 

 branch gives promise of producing such, 1 would spare it even if it bore visible 

 signs of infestation. If the cut actually exposed the galleries of the insect, I would 

 trim it down to a clean surface — to prevent the lodgement of water. Old hide- 

 bound branches bearing only weak shoots should be ruthlessly excised. 



I must own that I was, at first, insistent upon the burning of prunings and 

 opposed to their burial. But a careful study of the results has convinced me that 

 the latter is the sounder principle. 



Section of tea stem (xlO), showing entrance to gallery 

 of Xyleborus by ingrowth of cambial tissue. 



(a) bark, (b) cambium. (c) woody tissue, (d) section 

 of gallery, (e) ingrowth of cambial tissue blocking entrance 

 to gallery. 



