220 



PHYSIOLOGY OF GRGWl^H AND CONriGURATION 



Each zone of the elongating region of the root likewise passes through a 

 grand period of growth. In an experiment in which the primary root of a seed- 

 ling of Vicia faba was marked into millimeter zones, each zone being measured 

 after one, two, three, etc., days (the temperature being from i8° to 2i.5°C.), 

 the following daily increments of elongation of the youngest zone were observed. 



Number of Increment or 



Day Elongation, 



mm. 



1 1.8 



2 3-7 



3 I7-S 



4 17-5 



S I7-0 



6 14-5 



7 7-0 



8 o.o 



Fig. 102. — I, Crocus longiflorus. II, Oxalis. Z, contracting roots. Half natural size. 



Neither does the stem^ enlarge throughout its entire length, but the elongat- 

 ing regions are here much longer than in the root. The stem of Galium molligo 

 has a terminal region of elongation from 2 to 4 cm. long, embracing from 8 to 

 10 internodes; this region in, Aristolochia sipko is from 40 to 50 cm. long and em- 

 braces from 8 to 10 internodes; in Elodea canadensis it is from 2 to 3 cm. long, 

 with from 43 to 50 internodes; and in Hippuris vulgaris it is from 20 to 30 cm. 

 long. The single individual zones of the stem, as is true also of the root, elongate 

 unequally, and each passes through a grand period of growth. 



Leaf enlargement" is mainly basipetal, the enlarging region being situated in 

 the lower portion of the organ, near the stem. In the table below are given the 



'Askenasy, E., Ueber eine neue Methode, urn die Verthfiilung der WaohsthumsintensitM in wach- 

 senden Theilen zu bestimmen. Verhandl. Naturhist.-Med. Ver. Heidelberg a : 70-153. 1880. 



' Stebler, F. G., Untersuchungen liber das Blattwachsthum, Jahrb. wiss. Hot. 11 : 47-123." ig?8. 



