152 



GERMINATION, GROWTH, TISSUE TENSION. 



or in the case of a leaf with a regular network of lines crossing 

 at right angles. Waterproof Indian ink should be used, and the 

 marking may be done with a pen or fine 

 brush, or with special "space markers" 

 appliances for marking rapidly, con- 

 veniently, and without injury to the plant 

 any young parts into equal lengths or 

 areas which can be obtained from the 

 Bausch and Lomb Optical Company (Fig. 

 37). 



199. Distribution of Growth 

 in Root. When the root of a Bean 

 or Pea seedling has grown about 5 

 cm. long dry its surface if necessary 

 by stroking it with torn bits of blot- 

 ting or filter paper, and mark it with 

 transverse lines 2mm. (or, better, 1 

 mm.) apart, starting from the tip of 

 the root. 



Pin the seedling to the underside 

 of the cork of a wide-mouthed jar 

 with a little water at the bottom, or 

 to a piece of wood placed over the 

 mouth of the jar, so that the seed- 

 ling may grow in moist air ; or place 

 it in the bulb of a long thistle -tube, 

 the seedling being packed in with 



wet moss or cotton while the root grows down the tube 

 set the latter in a jar containing water, slanting the tube 

 with the marks on the root facing upwards so that they 

 may not be rubbed off as the root grows down the tube. 



Examine daily, and note that the marks just behind the 

 tip of the root become widely separated, while those farther 

 back change little or not at all. 



200. Distribution of Growth in Stem. Mark the 

 epicotyl of a Phaseolus seedling in the same way, starting 

 at the point where the two primary foliage-leaves are borne 

 and working down towards the cotyledons. The marking 

 may be done when the epicotyl is 5 cm. or even more in 

 length, because in stems the zone to which growth is 



Fig. 37 Space markers, for 

 making a row of lines (up- 

 per figure) or a network of 

 lines (lower figure) with 

 ink on growing organs 

 (Bausch and Lomb Opti- 

 cal Company). 



