2 
development of foliage he may be endangering the pro- 
duction of flowers. It is a common practice to reduce the 
apply of water so as to encourage the formation of flower 
buds. Some of our common British fruit trees when grown 
in tropical climes will develop into luxuriant trees with a 
wealth of foliage, but lack the flowers essential for the 
production of fruit. The practice of pruning and root 
pruning is based on the same phenomenon, and by reducing 
the amount of vegetative organs the formation of flower 
buds is encouraged. Yet though there seems to be this 
opposition between vegetative and reproductive organs the 
latter are really dependent upon the former. For it is 
only at the expense of the food material absorbed and 
worked up by the roots and leaves that the flowers are 
produced. The activity of the vegetative organs must 
therefore always precede the formation of flowers. 
This is seen very clearly in the case of annuals. These 
plants complete the whole of their life-cycle in one vegeta- 
tive season which is usually much shorter than a year, in 
some arid regions amounting only to a few weeks during 
and immediately after the wet season. An annual com- 
mences as a seedling at the beginning of the favourable 
vegetative season, and after the production of a limited 
number of leaves produces its flowers, which are kept sup- 
lied with food material by the activities of roots and 
eee until the seeds have matured, then the whole plant 
dies down to be replaced next season by the offspring 
developed from its seeds. Such is the life history of 
the mustard and cress and also that of most of our com- 
mon weeds like chickweed, groundsel, and some of our 
grasses. The ubiquity of our weeds is due not only to 
their effective means of dispersal, but also to their rapid 
growth to maturity which enables them to produce two 
and even three generations of plants in one season. 
Slower in their development and exhibiting a more 
marked contrast of vegetative and reproductive periods 
are the so-called diennials. In these plants after the vege- 
tative organs are produced they are employed throughout 
the first summer season in manufacturing and storing a 
large supply of food material, which is to be used in the 
formation of flowers and seed during the second year, 
after which the entire plant dies down having fulfilled 
its existence and produced a vast number of offspring. 
For the large store of food material which it has laid up 
