736 Botanical Microtechnique 



Many species of forest, orchard, and shade trees make excellent 

 preparations for the study of young woody stems. The basswood, 

 Tilia (Fig. 13.8 b) , has become a great favorite, but there is no advan- 

 tage in studying basswood in a region where it is not native. Species 

 of Populiis, Fraxinus, and Acer are easily sectioned. The apple and 

 other fruit trees have been neglected as class materials, although they 

 are easy to section. Tougher woods like oak, hickory, or locust are 

 much more difficult to cut, and complete j^erfect sections are not 

 obtained with such certainty. The standard coniferous subjects are 

 the white pines, Finns strobus in the east, and F. lambertiana or F. 

 flexilis and several other five-needle pines in the west. These are 

 representative of the five-needle or soft pines. For the hard pine type 

 many more species are a\ ailable, such as several species of yellow pine, 

 the scrub pines, and jack pines. There is not much choice among the 

 numerous two- and three-needle hard pines. 



The principal American genera of conifers should be represented 

 in a comprehensive stock of slides. Some of these trees are used as 

 ornamentals, the commonest ones being Abies, Larix, Tsiiga, Thuja, 

 Ficea, Fseudotsuga, and Jnniperus. Shrubby conifers are among the 

 commonest ornamentals, and specimens of shrubby species in the 

 genera Juniperus, Thuja, and Taxus are readily available. 



The methods of handling the woody dicots and coniferous stems 

 are decidedly stereotyped. The subdividing of such materials is 

 illustrated in Fig. 2.2. The impermeability of the cork on woody twigs 

 necessitates the use of a fluid of good penetrating powers, and FAA 

 has long been the standard fluid. Stems may be left in this fluid for 

 years. Preserved stems can be rinsed in several changes of 70% alcohol 

 at 1-day intervals and sectioned without embedding. The celloidin 

 method is recommended because of the ease and certainty of attaining 

 high productivity by (juantity production methods. 



Woody stems having bark tissues are usually stained with the 

 combinations recommended for herbaceous stems. Hemalum-safranin, 

 safranin-fast green, and safranin-aniline blue have become standard 

 stains. The method of handling sections and the staining jirocesses 

 are described in Chap. 8. 



Transverse, radial, and tangential sections of the cambial region 

 of woody i)lants make instructive j)rej)arations that are indispensable 

 for a critical study of the three-dimensional aspects of cambium, the 

 mechanism of abscission, and the structure of developing and mature 

 elements of the xylem and piiloem. 1 he excessive use of transverse 

 sections and the neglect of longitudinal sections build up an in- 



