458 THE BIOLOGY OF FLOWERING PLANTS 



instance is offered by Chusquea abietifolia, a climbing bamboo 

 described by Seifriz (1920). It flowers in cycles of 32 to 33 

 years, and as the flowering occurs over the whole of Jamaica 

 simultaneously, and is followed by death, the effect is 

 devastating. Bamboos of South Brazil flower in cycles of 

 13 years and Indian bamboos show similar conditions. 



In the biennial, accumulating food in its first year, in the 

 periodic mast years of the tree, in the long life of the Agave 

 before flowering takes place, we have clear indications that 

 manufacture of a certain minimum of food substance is a 

 necessary preliminary to reproduction. Another indication 

 is given by the familiar fact that in the year following an 

 unusually fine summer the flowering shrubs, hawthorn, 

 whin, broom, and the like are exceptionally rich. The 

 favourable conditions for photosynthesis have a delayed 

 effect — an instance of the principle of predetermination. 

 The initiation of the reproductive phase is therefore closely 

 linked with nutritional conditions, and it is, in fact, possible 

 to hasten, or delay, or suppress it altogether by appropriate 

 manipulation of the factors affecting the plant's nutrition. 



Many garden plants grown in the shade of trees fail to 

 flower ; neither ivy nor honeysuckle flower in the depth of 

 a wood. There is a well-known delay in the ripening of 

 cereals as the result of excess of nitrogenous manure. 

 Klebs (19 10, 1 91 8), as the result of extended investigations 

 chiefly on the house-leeks, concludes that the important 

 factor in flower formation is the ratio of assimilates to 

 salts, especially nitrates, at the disposal of the growing- 

 points. Predominance of nitrogenous compounds favours 

 vegetative growth, excess of carbohydrates favours reproduc- 

 tion. The same sort of cause is thus involved as is responsible 

 for the regulation of periodic growth. Hot, dry weather, 

 by favouring photosynthesis and depressing salt absorption, 

 tends to bring on early flowering, while humid conditions 

 with poor light depress assimilation and promote vegetative 

 growth. In his experiments with Seinpervivum Fiinkii 

 Klebs found that the plant, grown from a daughter rosette, 

 matures and will flower in the third or fourth year of its 



