1919] Hall-Goodspeed: Chnjsil 215 



rays will appear to be solidly filled with staiuable material. In the 

 vouuffer corkv lavers of the inner bark stainable cell inclnsions will 

 probably be nnmerous. Nearer the periphery a tissue which is often 

 intensely stained will usually be found, with greater magnification, to 

 consist largely of much crushed bark cells the suberized walls of which 

 take up the stain readily. Within the cell the rubber occurs in globular 

 form or in a more or less diffused state filling the entire cell cavity. 

 The globules may be large, one or two to a cell, or small and numerous 

 in each cell (cf. plate 18, figs. 4 and 5). Only this brief description 

 will be made here of the appearance of a typical preparation made 

 according to the process detailed above. The subject of the occurrence 

 of rubber in the plant and in the cell is treated of in some detail 

 elsewhere (cf. p. 234). 



As mentioned in an earlier paragraph, we have attempted with 

 some success to use the microscopical method for estimating the rela- 

 tive amounts of rubber in the various samples examined. A purely 

 arbitrary scale of values was adopted and relative rubber content de- 

 termined in each case by comparison with other preparations selected 

 as representing high, low, and medium rubber content. For such 

 comparisons a comparison-ocular was found to be useful. Tniformity 

 in the quality and quantity of the illumination is quite important 

 and artificial light was therefore used throughout. As soon as it 

 became possible to obtain large numbers of chemical analyses the 

 histological method of estimation became largely superfluous. How- 

 ever, in almost all cases it was resorted to prior to the chemical analysis 

 and a rough estimate made. Often when the rubber content of a sam- 

 ple appeared to be quite low no chemical analysis was made, and a 

 considerable amount of time and labor was thus saved. Throughout 

 the investigation we continued to examine microscopically numbers of 

 samples of doubtfully valuable species which were suspected by others 

 of containing rubber or which were collected by ourselves in order that 

 no possible source of rubber accessible to us should be overlooked. 



We have found the microscopical method invaluable in many phases 

 of this investigation. The ([uestion as to the place and time of the ori- 

 gin of rubber in the plant can only be answered by employing this 

 method. Furthermore, supplemented by chemical analysis it gives 

 important evidence concerning the parts of the plant which carry rub- 

 ber and their richness relative to age and location. Ultimately the sea- 

 son and method of harvesting such a rubber crop will be determined 

 largely on the basis of information so derived. 



