Increasing intensity of light induces increasing retarda- tion and arrest of growth. Under continued action of light of strong intensity the growing organ may undergo an actual Shortcniug.

In thch rcacticns thc action of stimulus of light resell}-

hch thv l-ll'ccta cl‘ vh-rtric and mechanical stimuli.

The ultra-viulvt rays induce the most intcnsc reaction in rvtartlatiun nf growth. 'l‘hc lcn's rcfrangihlc yellow and rurl rays itl‘l' practically incll'vctivc. But the infra-red 'ays ilulllcu a marked retardatian of growth.

’l‘lw vll'uvts nl‘ light and warmth arc antagnnistic. The l'crnwr induct-s a retardation and thc lattcr an acceleration

of growth.