392 



PHYSIOLOGY OF GROWTH. 



make out by repeated observations e.g. every quarter of an hour 

 that the tip of the plumule, when about 1-2 cm. long, is carried 

 round in space in a more or less circular line. I do not, however, 

 propose to study circumnutation, since the whole subject stands 

 in need of searching critical investigation, and especially more 

 attention than hitherto must be paid to the influence of external 

 conditions. 



1 See Sachs, Arbeiten d. bot. Inst. in Wurzburg, Bd. 1, p. 402. 



2 See Wortmann, Botan. Zeitung, 1882, No. 52. 



3 See Darwin, Movements of Plants. 



II. THE CONDITIONS NECESSARY FOR GROWTH 

 AND THE INFLUENCE OF EXTERNAL CONDI- 

 TIONS ON GROWTH MOVEMENT. 



158. Growing Plant Structures Require Material for Growth. 



The growth of a plant structure can only take place in a normal 

 manner when the necessary material and energy for the growth of 

 the individual cells are available. If, for example, seedlings 

 grow in complete darkness, the growth of the parts ceases when 

 the store of reserve material is exhausted. It is instructive to 

 study in some detail the connection between the energy with 

 which growth takes place and the stock of reserve material. For 

 this purpose we sow seeds of Phaseolus multiflorus in garden 

 earth in flower-pots. One pot is provided with as large seeds as 

 possible ; a second with similar seeds, from each of which, how- 

 ever, when germination has just begun, and the main -root has 

 broken through the seed-coat, one of the two cotyledons has been 

 removed. In a third flower-pot we sow small Phaseolus seeds. 

 Germination may take place in darkness or in the light. We find 

 that the plants derived from large seeds develop more vigorously 

 than those from small seeds, or from those deprived of one of their 

 cotyledons. In my investigations, which were conducted in the 

 light, there were at first no very striking differences in the ap- 

 pearance of the seedlings. Such differences did not appear till 

 the first trifoliate leaf had unfolded, and the third internode was 

 actively elongating. The plants derived from large seeds had 

 considerably larger leaves arid longer internodes than those from 



