202 BOARD OF AGRICULTURE. 



of cellular tissue penetrated by long bast cells, arranged parallel with the 

 axis of groAvth. I represents the place of the cambium or growing laj^er 

 of organizable material which descends from the leaves between the liber 

 and the sai^-wood during the period of growth. K is woody fibre which 

 gives strength to the stem, and through which the crude sap rises. L in- 

 dicates the vessels or ducts, with various markings, such as dots, rings, 

 and spirals, which are formed most abundantly in the spring, and usually 

 contain no fluid. They convey gases and aqueous vapors, and it may be 

 that a large proportion of all the water ascending from the roots to the 

 leaves jiasses through them as vapor. M is the layer of spiral vessels or 

 ducts which always inclose the pith, and in the young shoot extend into 

 the leaves and unite them to the pith during its life, which ceases with 

 the first season. 



Plate III., Figs. 1, 2, 3 and 4, represent the lilacs in the experiment of 

 Prof. Rainey. Fig. 1 shows tha condition of them all when a ligature of 

 copper-wire was placed upon them in the spring of the first year. Fig. 2 

 gives the appearance of a vertical section at the end of the first season, a 

 new layer of wood and of bark having been formed over the entire plant, 

 but in consequence of the compression of the Avire they are seen to be 

 much thinner below than above it. Fig. 3 illustrates the appearance of a 

 stem at the end of the second season of growth, the usual layers having 

 formed down to the ligature, but none below. Fig. 4 represents the sec- 

 tion of a specimen in June of the third year, the buds which had re- 

 mained plump all winter having now withered, and the part below the 

 wire being brown and dead. 



Fig. 5 exhibits the effect of removing rings of bark from a branch. 

 The rings of bark left on the wood at A do not increase at all, though 

 remaining fresh through one season of growth, while the rings marked 

 B are seen to have grown, particularly at the loA^er margin. The reason 

 is to be found in the fact that the former have no leaves to elaborate sap, 

 while the latter are furnished with these important organs of assimilation. 



Fig. G is a maple rootlet covered with absorbent hairs, excei^t near 

 the tip, which is pushed forward into the soil by the development of 

 new cells at a point a few lines from the very extremity. This j^enetrat- 

 ing end of the rootlet is seen to be furnished with loose epidermal cells, 

 marked B, Avhich are thrown off as the growth proceeds. At A is seen 

 a mass of earth filled with root-hairs. 



Fig. 7 shows the mode of constructing the mercurial gauge and attach- 

 ing it to a tree. At A is a stop-cock screwed firmly into the Sap-Avood to 

 Avhich the glass tubing is connected by couplings of iron. The gauge is 

 securely fastened to a scale, Avhich may be enclosed in a box. The tube 

 on the right may be lengthened and mercury added, should the pressure 

 necessitate it. When the mercury stands at the same level in both sides 

 of the inverted siphon, as at B, it is said to be at zero. In taking obser- 

 ■ vations, the difference in the number of inches of mercury in the two 

 sides is to be noted, and this Avill indicate the pressure or suction accord- 

 ing as it is observed in the right or left side of the bent tube. In record- 

 ing, the minus sign is prefixed to indicate suction into the tree. 



The draAvings for these illustrations were made by Prof. S. T. Maynard, 



