H2 PLANT PHYSIOLOGY 



salts are absorbed in abundance, the plant goes on growing in a purely vegeta- 

 tive manner ; either the rosette as such continues growing or lateral offsets are 

 produced, which behave in the same way (KLEBS, 1904, p. 266). 



2. When carbon assimilation is active in bright light, but when the absorp- 

 tion of water and salts is limited, flower formation takes place. 



3. When the absorption of water and salts is moderate in amount, it depends 

 on the intensity of illumination whether flowering or vegetative growth ensues. 

 If the intensity of the light be low (or if blue light be employed), growth only 

 follows ; if the intensity of light be increased (or if red light be used), flowering 

 takes place. 



There are many observations and experiments available which teach us 

 that light, nutrient salts, and other factors also are of significance in flower 

 formation. The significance of light in flower formation is shown by the well- 

 known fact that ivy forms flowers only in brightly illuminated situations, but 

 not in shady woods, although it grows well there. VOCHTING has obtained 

 similar results from experiments on Mimulus Tilingii. This plant left off 



1. 50 P. 364, 1. 25, for This illustration . . . environment.] read KLEBS 

 (1904, 548) has made corresponding experiments on such plants as Lobelia erina 

 and Veronica chamaedrys, and he shows that, in all plants that have no reserves 

 worthy of mention, diminution in light inhibits flower formation. He regards 

 the carbon assimilation induced by light as primarily responsible for its effect 

 on flower formation. This view is supported by the fact alluded to above that 

 blue light, under which assimilation is weakened, operates like light reduction, 

 while red light, which is more favourable to assimilation, permits flowering to 

 take place. It may further be concluded that blooming may occur in darkness 

 if only a sufficiency of organic materials be present, and that flowering can 

 also be induced by ringing, i.e. by preventing the flowing away of organic 

 materials. In addition to this assimilatory action of light, which has been noted 

 by other authors (LoEW, FISCHER, 1905), other effects, doubtless, must be taken 

 account of, e.g. its effect in promoting synthesis of proteids and other processes 

 whose nature is still obscure. 



Temperature also obviously plays an important part ; a continuous high 

 temperature retards flowering. Thus temperate plants remain in the vegeta- 

 tive stage in the tropics, and biennial native plants such as beetroot or Digitalis 

 may be prevented from flowering in the second year, if they be kept warm 

 during winter and allowed to continue vegetative growth. Thus KLEBS (1904) 

 has succeeded in making beetroot go on growing vegetatively for several years ; 

 similarily, Glechoma and Sempervivum grew for years in the vegetative state, 

 when they were prevented from passing into the winter resting condition. 



That air is essential to flower formation is shown by many aquatics, in which 

 only aerial shoots form flowers. It is quite probable that transpiration is of 

 considerable importance, for in land plants also transpiration appears to pro- 

 mote flowering (MoEBius, 1897). 



Finally, we must note the effect of nutrient salts. Many seedlings may be 

 induced to become dwarf and starved plants by withdrawal of nutrient salts, 

 and in these flowering often begins after a few stunted foliage-leaves have been 

 formed (p. 316). Experiments carried out by MOEBIUS (1897) have also shown 

 that grasses and Borago flower better when less mineral matter is supplied than 

 when they are richly manured. The increase in yield of fruit trees obtained 

 after pruning their roots must also be due to diminution in the mineral supply. 

 BENECKE (1908) especially has pointed out that all minerals do not operate in 

 the same way and from his own experiences and from the records published 

 by others he has proved that a diminution in the supply of nitrogen and an 

 increase in that of phosphorus lead to flowering. 



