INJURY TO THE LARCH BY SAWFLY 



LARVAE 



By Maud DeWitt Pearl 



PROFESSOR A. G. HARPER, 

 of Oxford, England, has re- 

 cently published the results of 

 a most thorough investigation 

 of the harm which Sawfly larvae do to 

 the larch. This pest first made its on- 

 slaught upon larches in England in 

 1904, attacking not only the European 

 larch but also species of the Japanese 

 larch, which had recently been intro- 

 duced into England. Most of the trees 

 investigated had sufifered defoliation 

 during several successive years. 



In order to study very accurately the 

 extent of injury wrought by defoliation, 

 a cross section from each tree was taken 

 regularly, every four or five feet apart, 

 depending upon the tree, from the base 

 to the to_p. A rectangular piece, from 

 8 to 12 mm. broad, was cut out of the 

 circumference at the four points of the 

 compass, the north side of the tree 

 having been marked previous to cutting. 

 A thin layer was cut from each one of 

 these blocks for microscopical examina- 

 tion and measurement. Three separate 

 sets of measurements were made for 

 ring growth and development of the 

 autumn wood on each layer, so that, in 

 all, twelve measurements were taken 

 for every cross section. The average 

 of these measurements was taken as an 

 indication of the mean radial enlarge- 

 ment of the tree at a particular height. 



The investigation showed that de- 

 foliation and consequent starvation re- 



sulted in a lessening in the amount of 

 growth of the annual ring and in a de- 

 crease in the thickness of the walls of 

 the cells forming the so-called autumn 

 wood. The decrease in ring growth 

 was more noticeable at the base of the 

 tree than at the tip, as would be ex- 

 pected. In cases of severe attacks ot 

 the larvae it was found that cambium 

 growth ceased entirely in certain parts 

 of the tree, particularly near the base. 

 The width of the ring of autumn wood 

 was not always lessened, but the outer 

 cell walls of this ring failed to thicken 

 while the inner walls presented a normal 

 appearance. The cause of this differ- 

 ence between the walls of the outer and 

 inner cells is not perfectly clear. Pos- 

 sibly the starvation which the tree suf- 

 fers through defoliation causes an ar- 

 rest of the development of the cells. 

 On the other hand there is an indication 

 that in some cases the second growth 

 of leaves which the tree very often 

 puts out after being attacked by the 

 larvae might possibly be the cause of 

 the thin walls. The growing leaves 

 draw heavily upon the water supply 

 and conditions at this time are similar 

 to those in early summer when the 

 regular leaf growth occurs and the so- 

 called spring wood, whose cells have 

 thin walls, is formed. 



Another condition which results 

 through defoliation is the formation of 

 abnormal resin ducts. 



Red Alder for Clothes Pins. 



Manufacturers have found that red alder from the Pacific coast is a suitable material for 

 clothes pins. Alder makes a white, smooth, springy pin. As a result of this fact, a clothes 

 pin factory, said to be the first on the Pacific coast, may be established at Portland, Oregon. 



Best Sight of Forest Fires. 



It is said that the best times of day to see forest fires from lookout stations are just 

 after daylight and just before sunset. •-• 



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