INT.] 



ON NORMAL GROWTH 



283 



MM. 



10 



MM. 



5 

 MM. 



They have recognized in the tip of the plant three growth 

 regions. At the extreme tip of the stem (or radicle) is the 

 region of rapid cell division but comparatively slow growth ; 



next below is the 

 zone exhibiting the 

 Grand Period of 

 growth ; and still 

 below is the zone of 

 histological differ- 

 entiation (Fig. 75). 

 In the lirst zone 

 growth of plasma 

 100AYS is occurring ; in the 



FIG. 75. Curve of daily growth in length of a disc, geconc l zone growth 

 originally 1 mm. long, and taken immediately behind 



the vegetation point of a radicle of Phaseolus. It OI the enchylema IS 



comes to occupy in successive days the three zones chiefly taking place; 



referred to in the text. From SACHS, Lectures on . , , i 



Plant Physiology. m the third ZOne 



there is growth of 



formed substance. The immense preponderance of the growth 

 of the second period (at 7 days) is an index to the preponderat- 

 ing influence in growth of the imbibition of water. 



\ 



3.0 

 2.8 

 2.6 

 2.1 

 2.2 

 2.0 



1.6 

 1.1 

 l. 



1.0 

 0.8 

 0.6 



U.I 



0.2 



_ 



X 



\ 



\ 



V 



\ 



0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 



FIG. 76. Curve representing the intensity of growth of roots of Pisum sativum, 



; Vicia sativa, ; and Lens esculenta, , the time being 



assumed to be constant. The length of the abscissas in the direction from left to 

 right corresponds to the distance, in millimeters, of the marked spaces on the root 

 from the root apex. The ordinates correspond to the amount of growth, in milli- 

 meters, of the corresponding piece of the root after 20 hours. From CIESIELSKI ('72.) 



That which occurs with one and the same piece of the stem 

 on successive days takes place simultaneously at the different 

 zones of the growing organ. Thus in the radicle (Fig. 76) 



