Int.] 



ON NORMAL GROWTH 



283 



•4- 



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 first zone 

 growth of plasma 

 is occurring ; in the 

 second zone growth 

 of the enchylema is 

 chiefly taking place; 

 in 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. 



Fig. 75. — Curve of daily growth in length oi a disc, 

 originally 1 mm. long, and taken immediately hehind 

 the vegetation point of a radicle of Phaseolus. It 

 comes to occupy in successive days the three zones 

 referred to in the text. From Sachs, Lectures on 

 Plant Physiology. 



0.5 1.0 1,5 2.0 2.S 



i.O 3.5 i.O Lb 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 heing 



assumed to he constant. The length of the ahscissae 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) 



