I9if»j Hall-Goodspecd: ('lirijsil 239 



As stated above we liave been unable to secure a sufficiently large 

 number of analyses of the younger and older portions of plants to 

 •make our conclusions as to regional distribution of rubber entirely 

 authoritative. The surprising decrease in rubber content a short 

 distance above the soil line is perplexing as is the succeeding increase 

 in the upper portion of the main trunk and branches. Elimination 

 of the primar.y cortex by peridermal activity in the older trunk 

 elements is obviously not an adequate explanation since at the soil 

 line maximum elimination of cortical tissue has taken place. Indeed, 

 cork formation with the accompanying distintegration of rubber cut 

 out thereby has progressed to a decided extent before the third 

 year of growth. The results obtained suggest, among other things, 

 a translocation of rubber or its derivatives. Such implications deserve 

 nothing more than a mere mention when the data are so fragmentary. 



h. SPECIFIC DISTEIBUTION IN MATURE TISSUES 



In an earlier paragraph it was stated that for making a rough 

 estimate under the microscope of the amount of rubber borne by a 

 given plant, a piece of mature tissue was cut from the main stem 

 axis. For convenience we may use as the basis for a description 

 of the tissues in which rubber, if present, may be expected to occur, 

 the accompanying photomicrographs and photographs of stained 

 preparations. As will be noted in plates — and — the stained areas 

 are for the most part extracambial although the ra^'s are also con- 

 spicuously stained. Anah'ses of one plant indicate that the amount 

 of rubber in the cortex as compared with that in the woody cylinder 

 is in the ratio of approximately six to one. 



Not all the stained areas without the cambium are rubber bearing, 

 however. Sudan Til stains intensely the walls of corky tissues and 

 the superficial portions of the stained material outside the woody 

 cj'linder represent cork and bark. Within this outermost layer the 

 broad wedge-shaped extensions of the primary rays are most conspicu- 

 ousl}^ stained. In a plant bearing from 4 to 5 per cent of rubber all 

 the cells of these ray extensions are filled with rubber inclusions. 

 Indeed in microscopical examinations of Chrysoihamnus these, areas 

 should first be examined for the presence of rubber as, uniformly, in 

 sections of stems over two 3'ears old, stainable rubber inclusions, if 

 present at all, will here be found. 



Bands of stained tissue will be seen connecting tangentially the 

 cortical ray extensions. These represent the parench^ymatous elements 



