46 STUDY OF COMMON PLANTS. 



appearance and structure in all parts of the stem. 

 Test the contents for starch. 



V. Having become acquainted with the minute anatomy 

 of the stem, study it from a mechanical point of view, 

 endeavoring to ascertain whether the thick-walled me- 

 chanical elements are grouped in such a way as to secure 

 strength with economy of material. Notice the disposi- 

 tion of the heavy sub-epidermal tissue in a continuous 

 hollow cylinder, the arrangement of the fibro-vascular bun- 

 dles, and the way in which the elements composing the 

 bundle-sheath are distributed. 1 



VI. Stem of white pine. The structure of the stem of 

 conifers presents various interesting peculiarities, but tho 

 arrangement of the parts and mode of growth are nearly 

 identical with those of dicotyledonous stems, and, moreover, 

 have been so fully treated in a number of laboratory guides 

 as to render it unnecessary to repeat directions for their 

 study. The student is recommended, however, to carry 

 out substantially the same plan of work on the stem of the 

 white pine as is outlined in the section on the Scotch pine 

 in Arthur, Barnes, and Coulter's Plant Dissection. 



VII. Cambium. Nearly all woody species in temperate 

 regions of the globe form distinct annual rings which 

 mark the growth of the wood from year to year. In order 

 to understand the process a study of the cambium should 

 be made. Shoots of the white pine four or five years old are 

 suitable for this purpose. They should be cut during the 

 season of active growth, say from June to August, and 

 placed in alcohol. If properly hardened, transverse sec- 

 tions may be obtained that show very perfectly the new 

 wood and bark formed by the division of the delicate 



1 Cf. Strasburger, Practical Botany, p. 88, and footnote. 



