134 GRAND PERIOD. [CH. VI 



the graduated edge of the scale can be brought close 

 to the surface of the root to be marked. 



Pin the bean with 2 or 3 others similarly treated in a 

 jar half filled with water, the roots being in damp air. 



After 12 — 15 hours measure the distance between the 

 marks. The result will show that the most rapidly 

 growing part of the root is a short distance behind the tip. 



(172) Distribution of growth in air-roots. 



In aerial roots the region of growth is of much greater 

 extent. Mark the air-root of an Aroid {e.g. Philodendron) 

 at intervals of 5 mm. for a space of 30 mm. from the tip ; 

 white paint, such as Aspinall's Enamel, is useful for 

 marking the dingy coloured roots of these plants. Measure 

 again after 2 days. 



(173) Distribution of growth in flower-stalks, etc. 



For this purpose the scape of the cowslip is useful: 

 select a straight-growing stalk, of which the flowers are 

 still in bud, gather it carefully (by cutting not by pulling), 

 and mark it at intervals of 5 mm. Keep it in a corked 

 test-tube, with a little water at the bottom, for 12 — 18 

 hours. 



Vigorously growing shoots of Valerian may be treated 

 in the same way, i.e. cut and grown in damp air. 



Plants of Phaseolus in pots, having 2 or 3 internodes 

 developed, are also useful : the marked internodes should 

 not be cut, but left on the plant. 



Here as in the case of the root we get evidence of the 

 "grand period"; the youngest part of the stems has 



