PRACTICAL HINTS 



balsam or glycerine jelly. Sections when used in the lantern, 

 either mounted or unmounted, should always be protected by an 

 alum bath. I have had many ruined by inexperienced operators. 

 Sections of Hornbeam, Maple, and some other woods have a 

 curious way of stretching prodigiously, owing to the lateral 

 dilation of the cells of the rays. In contracting to their former 

 size during drying they pull themselves to pieces, hence it is 

 necessary to detach them from the glass on which they have 

 been wetted while they are still moist, and to dry them without 

 pressure. 



I much prefer to examine the sections unmounted, i.e. dry, 

 as the colours are changed by balsam and the detail is more 

 difficult to see, moreover the gums and resins contained in the 

 pores become dissolved in the process of preparation and the 

 specimen loses much of its character. For the same reason I 

 never stain a section except as an additional expedient. The 

 purposes for which the thin sections are specially useful are to 

 measure and count the rays and pores, to detect soft-tissue 

 otherwise invisible, to decide whether the rays are of one or more 

 rows of cells, and if they are denser or laxer than the surrounding 

 tissue : all most valuable items of information from a scientific 

 and descriptive point of view, and sometimes decisive in the 

 matter of settling a doubtful point in identification, yet in 

 practice rarely absolutely essential. 



Measurement is the chief among these points, as in a by no 

 means small number of orders the breadth of the rays ranges 

 within certain definite limits. The conspicuous breadth of those 

 of the Oaks, which can be measured with a rule, is markedly 

 characteristic of the genus Quercus, and the same may be said 

 of the whole of the order Proteaceae or Silky Oak family. The 

 other extreme is represented by the Australian Gum trees 

 (Eucalypti), whose rays are so narrow and so numerous that they 

 may occur to the number of twenty-two in the space of i mm. 

 The pores in their turn range from less than i to 400 per 

 sq. mm., and in the matter of size their variation is only less 

 great than that of the rays, as, in the wood of the Silk-cotton 

 tree (Bombax malabaricum), they are as large as pin-holes, 

 while in the Common Boxwood, they can scarcely be counted 

 under a two-inch lens. The measurement may be carried out 

 with a micrometer, such as is used for microscopical purposes. 

 This may be essential to the investigator, but I limit myself here 

 to the tabulation of the various sizes by groups, after the 

 manner of Nordlinger and Gamble. I have been urged to drop 

 these empirical groups and to give the exact measurement in mm., 

 but my aim and ambition is to interest many who are not pro- 

 fessed botanists, and to bring to the work some who have had 



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