282 GROWTH 



parenchymatous tissues of Trade scantia, Cyptipedium or some 

 other orchid and observe the character of the large nuclei. 

 Constrictions are shown that more or less nearly divide the 

 nucleus in parts, and this may have been repeated several times, 

 and some of the cells may be seen to contain many nuclei, if the 

 sections are fixed with acetic methyl-green. 



Direct division of the nucleus is often induced by the presence 

 of endophytic fungi, either as parasites or symbionts, and may be 

 seen in the mycorhizal rhizomes of Goody era. 1 



361. Course of Growth in Cells in the Apical Regions of Roots. 

 Secure slides of longitudinal sections of root tips prepared by the 

 imbedding method. Some should be stained with nuclear and 

 others with cytoplasmic dyes. Cells may be seen in the suc- 

 cessive stages of division and growth. Follow the course of the 

 cells in the periblem cylinder. Note that an approximate cubical 

 form is preserved as long as the cells are in the dividing stage, as 

 indicated by the presence of mitotic figures. Measure these cells 

 and make exact drawings with a camera lucida, showing the out- 

 lines of the nuclei of cells in the dividing zone, but which are 

 temporarily at rest. Make similar drawings of cells which have 

 ceased to divide. Follow the course of the nucleus several cm. 

 from the tip in the cortex and ascertain whether it increases or 

 decreases in size. Make estimates of the increase in size of the 

 cell. Ascertain the amount of elongation of the cells at dis- 

 tances of I mm., 2 mm., 3 mm., 4 mm., 5 mm., etc. From the 

 apex and from the rate of growth of the roots at hand, estimate 

 the age, at which increase ceases (Fig. 133). 



Plot a curve which would show the relative rates of elonga- 

 tion of the cells in the different zones denoted above. 



362. Measurement of the Growth of the Apical Portion of a Root. 

 Germinate seeds of Zea, Pisum, or Phaseolus and select a few seed- 

 lings with roots about 2 cm. in length, and lay on a piece of 

 moistened cork. Place a thin metric scale alongside the root, and 

 mark into intervals of 2 mm. beginning at the tip, by means of a 



J MacDougal. Symbiosis and saprophytism. Annals of Botany. 13: I. 18)9 



