BY M. P.. WELCH. 



481 



Some of tbe exudation from a cut stem was transferred to a slide and, 

 as before, solution occurred in 95%-100%, usually in the former. In some 

 cases a very small, clear, tilm-like residue was left, which was insoluble in 

 chloroform or ether. 



.Sections of fresh leaves stained in a solution of alkannin in 50% alcohol 

 showed the characteristic bright red colouration in tbe ducts, indicating the 

 presence of oil. Cyanin in oO^p alcoliol also gave a positive reaction for oil in 

 the central ducts. Glacial acetic acid, and also aqueous solution of chloral 

 hydrate gave complete solution. The Unverdorben P^-anchimoiit reaction (Zim- 

 merman), using copper acetate, showed the normal colouration for terpenes. 

 Tests for tannin gave no indications in the central ducts or in the adjacent cells. 

 There seems no doubt that oil occurs in these central ducts, and is similar, at 

 any rate in behaviour under microehemieal tests, to that occurring' in the normal 

 glands in the mesophyll of the leaves or in the cortex of stems and jjetioles. 



Some material of E. cort/mbosa was soaked in water for six months and 

 at tlie end of this period the contents of the duets were still soluble in 95% 

 alcohol, showing apparently no alteration in this respect. Nevertheless material 

 fixed in '•chromacetic acid," yni-iif acid in 50% or 95% alcohol, "formalin 



Text-fig. ". — Ducts in section showing the insoluble residue, (a) and (b) in 

 y stage of development, (c), (d) and (e) later stages in which a lining is 

 nd in the cavity. 



early stage _. ,.- . _ 

 found in the cavity 



alcohol" or even ordinai-y 95% alcohol, shows an insoluble residue, often in the 

 form of a complete ring surrounding the duct when seen in section (Text-fig. 7 

 c-e), or in tlie cells. It is also noticeable in sections cut from dried leaves. 

 This insoluble residue is sometimes found scattered irregularly in the duct, ap- 

 parently retaining the outline of the cells in which it was at one time enclosed 

 (Text-fig. 7 a, b). It is apparently an oxidation product derived from the 



