230 EXPERIMENTS WITH PLANTS 



are they larger, but the water meets with no obstruc- 

 tions in passing through them, while in the smaller 

 cells there are cross-walls at frequent intervals through 

 which it must pass. Such cross -walls occur also in 

 the ducts at an early stage of their development, but 

 they are soon broken down and absorbed, and we find 

 only remnants of them in the form of rings here and 

 there on the walls of the ducts (as shown in Fig. 

 133). 



On comparing a fibrous bundle of the Corn (Fig. 

 134) with that of the Squash, we find also two large 

 ducts (d,d), together with (usually) an annular tra- 

 cheid (a) and a spiral one (sp), beside which is a large 

 air-space, the effect of a tear in the tissues caused by 

 rapid growth; the rest of the wood consists of wood 

 parenchyma (wp) . 



Let us now investigate the wood of an Oak (or 

 other hardwood tree such as Hickory, Chestnut, Ash, 

 Acacia, etc.) and of a Pine (or other softwood tree 

 such as Spruce, Cypress, Juniper, etc.) by first 

 tracing the path of the water (by means of eosin 

 solution) and then examining sections under the micro- 

 scope. Cutting sections of woody stems presents 

 certain mechanical difficulties, but these are easily 

 overcome if we choose young sterns (not more than 

 two or three years old) and trim the surface to be 

 cut until it is not more than an eighth of an inch in 

 diameter. 



