286 THE INDUCTIONS OP BIOLOGY. 



sepals, and petals, and stamens, follow each other in close 

 succession, instead of being separated by portions of the still- 

 growing axis. Another group of evidences meets us 

 when we observe the variations of fruit-bearing which accom- 

 pany variations of nutrition in the plant regarded as a whole. 

 Besides finding, as above, that gamogenesis commences only 

 when growth has been checked by extension of the remoter 

 parts to some distance from the roots, we find that gamo- 

 genesis is induced at an earlier stage than usual by checking 

 the nutrition. Trees are made to fruit while still quite 

 small by cutting their roots or putting them into pots; and 

 luxuriant branches which have had the flow of sap into them 

 diminished, by what gardeners call " ringing," begin to pro- 

 duce flower-shoots instead of leaf-shoots. Moreover, it is to 

 be remarked that trees which, by flowering early in the year, 

 seem to show a direct relation between gamogenesis and in- 

 creasing nutrition, really do the reverse; for in such trees 

 the flower-buds are formed in the autumn.. That structure 

 which determines these buds into sexual individuals is given 

 when the nutrition is declining. Conversely, very 

 high nutrition in plants prevents, or arrests, gamogenesis. 

 It is notorious that unusual richness of soil, or too large a 

 quantity of manure, results in a continuous production of 

 leaf -bearing or sexless shoots; and a like result happens 

 when the cutting down of a tree, or of a large part of it, is 

 followed by the sending out of new shoots: these, supplied 

 with excess of sap, are luxuriant and sexless. Besides being 

 prevented from producing sexual individuals by excessive 

 nutrition, plants are, by excessive nutrition, made to change 

 the sexual individuals they were about to produce, into sexless 

 ones. This arrest of gamogenesis may be seen in various 

 stages. The familiar instance of flowers made barren by the 

 transformation of their stamens into petals, shows us the 

 lowest degree of this reversed metamorphosis. Where the 

 petals and stamens are partially changed into green leaves, 

 the return towards the agamogenetic structure is more 



