MOVEMENTS OF GROWTH. 385 



in which, after a certain time (say twenty hours), any growth 

 is found to have taken place, is always very small. According 

 to the kind of seed, viz., and the individuality of the separate 

 objects, the growing region of the root (e.g. in Pisum, Phaseolus, 

 etc.) is only about 4-8 mm. in length. The growing region of 

 the stem, on the contrary, is, as we shall see, much longer. 1 



We now proceed to follow closely the grand period of growth 

 in the stem, and there is no special difficulty in determining the 

 general course of the growth in this organ. We grow seedlings 

 of Phaseolus or Pisum, rooted in loose garden earth, in absence 

 of light, keeping the temperature as constant as possible. By 

 single measurements made from day to day it can be proved 

 that the internodes (the epicotyl or succeeding internodes) at 

 first grow slowly, then more rapidly, at a particular time exhibit 

 a maximum rate of growth, and then again grow more slowly. 

 Seedlings growing in darkness (I experimented, for example, with 

 Pisum plants, produced from large seeds) may, under some 

 circumstances, .produce very long stems, consisting of quite a 

 large number of internodes. One plant which I had under 

 examination produced a stem more than 500 mm. in length, 

 and composed of seven internodes. If we measure the length 

 of the mature internodes we find that the oldest are compara- 

 tively short, then come longer ones (in my experiments the 

 fifth was the longest), and the youngest internodes are then 

 again shorter. It is very generally observable that the successive 

 internodes, when fully elongated, are not of the same length, 

 a fact which finds a simple expression when we say that the 

 growth energy of the different segments of the stem varies, owing 

 to internal causes. 



We grow seedlings of Phaseolus multiflorus in the dark in 

 flower pots. When the epicotyls have attained a length of about 

 50 mm., we make, on the most strongly developed stems, a 

 number of ink-lines at intervals of 3 to 5 mm. (for method 

 see 147 and 148). The seedlings are then again placed in the 

 dark, the temperature being kept as constant as possible. Every 

 twenty-four hours we determine by measurement the amount 

 of growth in the different partial zones. The growing region 

 of the stem, in contrast with that of the root, is very exten- 

 sive. I found, for example, that a length of 35 mm. of the 

 Phaseolus epicotyl was in a state of growth. In the youngest 

 (uppermost) partial zone, the growth at the beginning of the 



P.P. C C 



