26 BOTANY. 



ory, elm, ash, poplar, willow, and basswood, and note the differences 

 in tlie amount and compactness of their fibrous tissue. 



(/) To isolate the wood-fibres, make a number of sections as in (a) 

 above, then heat for a minute or less in nitric acid and potassium 

 chlorate. The fibres may now be separated under a dissecting mi- 

 croscope, or the specimens may be transferred to a glass slide and 

 dissected by tapping gently upon the centre of the cover-glass. This 

 is known as Schulze's maceration. 



44. Milk-tissue {Laiiciferous Tissue). — In many fami- 

 lies of flowering plants tissues are found which contain a 

 milky or colored fluid — the latex. For the sake of sim- 

 plicity two general forms may be distinguished: (1) that 

 composed of simple or hrancJiing tubes (Fig. 16), which are 

 scattered through the other tissues. As found in the 

 Spurge family, they are somewhat simply branched and 

 have very thick walls (Fig. 16, B); in other plants they 

 are thin-walled and are sometimes inclined to anastomose. 

 They extend through the other tissues of the plant, and 

 have a growth of their own, branching and elongating as 

 if they were independent plants. They contain proto- 

 plasm, and have many nuclei. 



45. (2) The other form is that composed of reticulately 

 anastomosing vessels. Here the tissue is the result of the 

 fusion of great numbers of short cells. The walls are thin 

 and often irregular in outline. In chicory, lettuce, etc., 

 this form of milk-tissue is very perfectly developed as a 

 constituent part of the outer portion of the woody bundles 

 (Fig 17, A and B). 



46. The latex of different plants contains different sub- 

 stances ; thus in many spurges (Euphorbiaceae) and milk- 

 weeds (Asclepiadacese) it contains caoutchouc, which yields 

 india-rubber ; in poppies it contains opium ; in some cases 

 alkaloid poisons are present, while in still others, as the 



