HARDWICKE'S SCIENCE-GOSSIP. 



275 



>up the stem, seldom entwining in a screw-like 

 manner, as in the case, of the woodbine. The 

 smaller leaders of the ivy encircling the stem as they 

 increase in growth and thickness become so tight 

 upon the stem as to prevent the natural expansion of 

 the bark ; hence the annual layers of the wood are much 

 less should the ivy not be removed and allowed to 

 grow unchecked. The annual woody layers become 

 less and less, and ultimately become scarcely trace- 

 able. The ascending sap also becomes less and less, 

 •and the leaves turn smaller, paler, and decay sooner. 

 They also expand later, and feeble terminal shoots 



Fig. no. — Stem of Common Alder showing bulges caused by 

 Woodbine. The arrows indicate the course of the descending 

 sap. 



are produced, in short the whole system is affected 

 and sadly crippled, and as a natural result, the tree 

 dies. 



Woodbine, or honeysuckle, differs in its growth 

 upon trees from taking quite a serpentine habit, 

 seldom growing upon the stem in a straight manner. 

 From the habit of growth, many curious turns and 

 bulges are found in woods where this twiner is 

 allowed to grow unchecked. The illustration given 

 herewith represents a correct drawing from a com- 

 mon alder growing by the water's edge. The wood- 

 bine had died away, and no traces of it could be 



found ; but from the specimen, evident proof is shown 

 of its damaging effect. A b the stem, c the branches, 

 d ef ^ are bulges caused by the twining of the wood- 

 bine. By referring to d this bulge is nearly round 

 and round ; this is caused by the creeper being 

 almost directly round the stem, preventing the ex- 

 pansion of the bark, and checking the descending 

 sap ; e and g are in more of a slanting direction. 

 This sort of form is the commonest to be found ; g 

 is where the woodbine was in so much a longer circle 

 than either of these described, that the creeper did 

 not offer so much resistance to the bark when ex- 

 panding, hence there is less bulge. When the creeper 

 is nearly horizontal round the stem, the largest bulges 



A 



TO 



1 



Fig. in. — Tree stem showing the direction taken by Ivy 

 stems and branches, with which it is covered. 



will be formed. Again, suppose a stem of ivy, three 

 inches diameter, to be growing up the side of the 

 stem of a larch or other tree, when the bark expands 

 to allow of the yearly deposit of wood, the ivy is 

 gradually pushed out with the bark, and no bulge is 

 produced on the stem ; but, again, should thick 

 branches ramify round the stem so as to completely 

 encircle either a stem or a branch, the bark will 

 expand so far yearly as the ivy will allow with free- 

 dom ; then gradually the ivy will offer great resistance 

 to the bark, and if not removed at this stage, bad 

 results are sure to be looked for. 



In the case of the woodbine, however, the result 

 is somewhat different, as the stem of the tree increases 

 in thickness, as also does the stem of the woodbine. 



