THE INNER LIFE OF PLANTS. 319 



an all-important part in the economy of plants every school-boy 

 knows. The bleached, or, as it is technically named, " etiolated," 

 appearance of the potato-leaves which have grown in a damp and 

 darkened cellar, is familiar to all. Instead of presenting their nor- 

 mally green appearance, the potato-leaves are yellow ; and instances 

 of the blanching of esculent plants by the gardener, through the 

 influence of darkness, are too familiar to require mention. It is 

 not too much to say that light is absolutely necessary under 

 ordinary circumstances for the growth of plants. Only in the 

 presence of light can the green-colouring matter, or "chlorophyll," 

 of plants be developed ; and, as this substance plays an important 

 part in the nutrition of plants, the absence of light simply means 

 starvation or death to all normally green plants. Curiously enough, 

 however, light is known to retard plant-growth, even whilst it is 

 essential for the performance of the chemical actions through which 

 ordinary plant-life is maintained. Potato-stems grown in a dark 

 cellar, for instance, are much longer than the ordinary stems grown 

 in the light. When a plant is subjected to light from a window, the 

 side of the stem farthest from the light grows longer than the oppo- 

 site side, and as a result the plant curves towards the light. Such a 

 feature is paralleled in the animal world by the habit of sea-anemones, 

 which, when confined in a clear glass vessel, shift their position 

 towards the light when they have been deprived of the light-rays by 

 changing the situation of the vessel ; and the little hydras of the pools 

 and ditches similarly congregate invariably on the side of their glass 

 which is next the light. Most parts of plants, in their natural growth, 

 possess this habit of curving towards the light ; and such a habit has 

 been appropriately named " positive heliotropism " by the scientific 

 botanist. The well-known legend of the sunflower (Helianthus\ that 



Mad Clytie, whose head is turned by the sun, 



will naturally be brought to remembrance by the recital of the sober 

 facts of physiological botany. Churchill's description of the sun- 

 flower as 



The proud giant of the garden race, 

 Who, madly rushing to the sun's embrace, 

 O'ertops her fellows with aspiring aim, 

 Demands his wedded love, and bears his name, 



forms, after all, by no means an inapt commentary on this curious 

 plant-habit, which is paralleled by the observation of the equally curious 

 habit of the corn, the ripe ears of which incline to the south, and rarely, 

 if ever, turn northwards. So also the curious " compass-plant " of 

 America (Silphium) may be said to illustrate a similar or analogous 

 habit. It is this plant which Longfellow speaks of as 



