MOVEMENTS OF GROWTH. 



387 



1 See Sachs, Arbeiten d. botan. lust, in Wilrzlmrg, Bd. 1, p. 413. 



2 Ditto, Ed. 1, p. 99, and Wortmann, Botan. Zeitung, 1882. 



3 See Prantl, Arbeiten d. botan. Inst. in Wiirzburg, Bd. 1, p. 371. 



155. Rate and Energy of Growth. 



Daily experience teaches us that the rate of growth of plants 

 varies very considerably. Even the separate individuals of one 

 and the same species under similar external conditions, exhibit 

 different rates of growth. The experi- 

 menter has always to take account in his 

 researches of individual differences of 

 behaviour in the objects under investiga- 

 tion, such differences often influencing the 

 success of the observations in a very un- 

 pleasant manner. It is therefore instruc- 

 tive to make the following experiment; 

 Peas, beans, or other seeds, as normal and 

 uniform as possible, are germinated in 

 large numbers in damp sawdust. After 

 some time, accurate measurements of roots, 

 stems, and leaves are made, and from these 

 we learn that corresponding organs of 

 different individuals of the same species, 

 in spite of their having all developed 

 under precisely the same external con- 

 ditions, have by no means grown at the 

 same rate. The individual differences of 

 behaviour in the separate plants, which 

 are often considerable, are clearly brought 

 out in such observations. 



Under similar external conditions, how- 

 ever, homologous organs of different species 

 of plants also exhibit specific differences 

 in their rate of gowth. The stems and 

 leaves of Aristolochia Sipho and Humulus 

 lupulus, for example, grow comparatively 

 rapidly ; the corresponding organs of other 



. FIG. 128. Apparatus for 



plants very slowly. Again, the stems, e.g. investigating the growth of 

 in Polygonum Sieboldi, grow very rapidly. root8 ' 

 I found, e.g., that a shoot of this plant, which on May 3rd was 

 60 cm. high, had, after twenty-four hours in warm, damp 



