160 Practical Plant Biology. 



Take the half of the stem which has been soaking in the dilute nitric acid, 

 wash it and with the head of a large pin carefully scrape away the axial column 

 of fundamental tissue and expose the net-work of large conducting, tracts from 

 the inside. These will appear pink, while the fundamental tissue is coloured 

 deep orange by the acid. Where the section runs longitudinally in a leaf- 

 base the tracts passing down it may be displayed by scraping away the 

 fundamental tissue and even their connection with the sides of the mesh 

 corresponding with the leaf-base may be ascertained. A sketch should be 

 made of the net- work of conducting tracts and of its branches. 



Cut a transverse section of a leaf-stalk. Mount in water and cover. If 

 permanent preparations are desired the sections, from fresh material, should 

 be soaked for some minutes in spirit, and then washed in water. If material 

 preserved in spirit is used the sections may be placed in water immediately ; 

 select out the thinnest of the sections and they must be very thin and place 

 them in a staining- glass containing a mixture of watery safTranine and 

 Delafield's haematoxylin. When they are sufficiently deeply stained, i.e. in 

 ten minutes to half an hour, wash in water and pass through two changes of 

 spirit to anhydrous spirit which must be closely covered. Anhydrous spirit 

 may be prepared by putting roasted copper sulphate into ordinary spirit. 

 The anhydrous copper sulphate dehydrates the spirit in contact with it. The 

 volume of the roasted copper sulphate should be at least about quarter that of 

 the spirit treated. In this way most samples of commercial spirit may be 

 rendered sufficiently anhydrous. Of course the spirit, during treatment and 

 till use, should be kept in a tightly- stoppered bottle. From the anhydrous 

 spirit the sections should be transferred to oil of cloves. In this at first it is 

 necessary to keep the sections forcibly submerged. Otherwise they come to 

 the surface and absorb water from the atmosphere. When the sections have 

 become quite clear the surplus oil should be removed from them by touching 

 them with absorbent paper. They may then be placed in a drop of Canada 

 balsam on a slide and covered. 



The general outline of the leaf- stalk is convex on the lower side and flat 

 or even slightly concave on the other. The greater part of the section is 

 composed of fundamental tissue. The outer layers are thick walled and 

 sclerenchymatous, and form the sclerenchymatous tubular casing of the leaf- 

 stalk. In the unstained section these walls are colourless ; they take a red 

 colour from the staining mixture. The walls of the inner fundamental tissue 

 are much thinner. Their outline is circular in the transverse section. They 

 take a purple colour from the stain. Embedded in the thin- walled fundamental 

 tissue are the cross sections of several conducting tracts. They are circular 

 or oval in outline. The wood-tracheids have thick walls which stain red, the 

 bast walls are thin and stain purple, while the bundle-sheath has walls which 

 are orange-brown in colour. A drawing of one conducting tract should be 

 made under the high power. 



Next prepare a transverse section of a pinnule. This may be most easily 

 done by rolling several pinnules in a tight cylinder in order to give mutual 

 support. Sections of this cylinder may now be cut with a razor and 

 floated out in water. A large number should be prepared and the thinnest 

 selected mounted in boiled water and covered for examination. When a 

 suitably thin section is found it should be sketched and the drawing should 

 show the upper epidermis, the palisade and spongy parenchyma and the lower 

 epidermis. Also the position of the conducting tracts should be marked. 



Portions of the upper and lower epidermis should be sliced off other pin- 

 nules and mounted. These will show the peculiarly shaped epidermal cells 

 and the stomata. Estimate the size of the stomatal openings with the 

 Ghost-micrometer. 



