FIBRO-VASCULAR BUNDLES. 13 



with the figures in Part I. In order to identify some of the 

 structural elements composing a bundle, it is sometimes advis- 

 able to resort to cautious maceration (see 70), so that the parts 

 may be isolated. It has been found advantageous, in a few in- 

 stances, to very securely fasten the section under examination to 

 thin rubber membrane by means of the best " rubber" cement 

 or marine glue, and then subject the membrane and section to- 

 gether to the action of the macerating liquid, great care being 

 exercised to have the process gradual. After the maceration is 

 complete, the membrane is removed from the liquid, washed, 

 and then slowly stretched until the adherent wood-elements are 

 somewhat torn apart. It will be observed that by this method 

 their former relations need not be greatly disturbed. 



After examining the fibro-vascular bundles in the seedlings 

 above named, proceed to the study of the bundles in the roots, 

 stems, and leaves of two adult herbaceous plants, for instance 

 Indian corn and Bean, in order to ascertain what differences, if 

 any, exist in the composition of the bundles in a given organ at 

 different periods of growth. 



It was stated in 309 that the simplest form of a fibro-vascular 

 bundle consists of merely a few tracheal cells (or sometimes tra- 

 cheae) together with some cribrose or sieve cells. The student 

 should search for tracheids, which may occur disconnected from 

 any bundle ; as for example in the stems of species of Salicornia 

 (a seaside plant of succulent texture), and in the petiole and 

 pitchers of Nepenthes. Tracheids occur also, often in a con- 

 tinuous layer, as a sheath of the aerial roots of orchids. Sieve- 

 tubes may be looked for at a little distance from the bundles in 

 the stems of potato and tobacco, where they occur in the periphery 

 of the pith. 



Two supplementary studies are strongly advised : (1) of the 

 bundles in tVrns, (2) of those in aquatic phaenogams. In the 

 former, " conc-entric " bundles are met with ; in the latter, rudi- 

 mentary bundles. 



II. COUESE OF THE BUNDLES. 



The course of the fibro-vascular bundles can be traced in some 

 cases, especially in young and rather juicy stems, like those of 

 Impatiens, with little or no difficulty ; but it is generally neces- 

 sary to treat somewhat thick sections of the stem under ex- 

 amination by a macerating liquid, for instance potassic hydrate, 

 after which the course can be made out. In most cases the 

 course of the bundles can also be made out by series of sections 



