METABOLISM IN LIVING PLANTS. 461 



fruits owe their colour. On the other hand must here be mentioned that scarlet-red 

 colouring-matter, as yet little known, probably belonging to the anthracenes and 

 allied to the madder-red, which perhaps serves to frighten animals, and which is 

 so pronounced, for example, in the accrescent calyx surrounding the fruit of the 

 Winter Cherry (Physalis Alkekengi). 



Besides the colouring -matters, sweet-tasting substances, especially cane-sugar, 

 and also mannite and dulcite, play an important role of a similar nature. Although 

 their function can only be discussed in detail later on, it is nevertheless well 

 to point out here that the distribution of the spores of Ergot of Rye (Claviceps 

 purpurea), for example, is brought about by means of a sweet fluid excreted by the 

 mycelium, which is eagerly sought for by ants and other insects. The insects in 

 sucking and licking up this fluid carry off the spores of the Ergot, and then deposit 

 them on other plants. Countless plants secrete sweet honey in certain parts of their 

 flowers, which serves to attract bees, humble-bees, and butterflies, whose task is to 

 carry the pollen from flower to flower. Certain animals, on the other hand, whose 

 visits would be injurious to the flowers, are kept away, or still better, diverted from 

 them by the honey secreted at the base of the foliage-leaves, which serves as a 

 counter-attraction. 



The numerous ethereal oils, resins, and balsams have a like significance for the 

 life of the plant. The ethereal oils are principally hydrocarbons, only a few con- 

 taining oxygen in addition; oils of lavender, cumin, and eucalyptus, oil of turpentine 

 and camphor, and many others consist of ten atoms of carbon and sixteen of 

 hydrogen. In spite of this similar percentage they differ very markedly in their 

 optical properties, their boiling point, and particularly in their smell, as can indeed 

 be observed from the few examples cited. There are some plants whose foliage, 

 flowers, and fruit contain ethereal oils having different odours, as, for example, the 

 Orange-tree, whose leaves yield "petit grain", the flowers neroli, and the fruit oil 

 of orange. But since these three oils contain the same number of carbon and 

 hydrogen atoms, it must be assumed that their difference depends upon the varying 

 arrangement of the atoms in a molecule. The majority of these oils are trans- 

 formed into resin by the addition of oxygen, or mixtures of volatile oils and resms 

 are produced, which are called balsams. Volatile ethereal oils, which are perceived 

 by the olfactory nerves even at a distance, function in part as means for alluring 

 animals which benefit the plants in question by transferring the pollen or 

 disseminating the fruits, seeds, or spores; but they also function in part as measures 

 for protecting the plant against attacks from the animal kingdom. The latter is 

 the case especially in foliage-leaves with powerful odours, and in resinous fruits, 

 and these are not used by animals as food. Balsams, which cover foliage-leaves 

 issuing from the buds like a varnish, form a protection against excessive trans- 

 piration, and also render material help in the absorption of water by the leaves, as 

 has been already described. The viscous excretions, formed of a mixture of resin 

 and mucilage on the stems and leaf-stalks, which are formed so abundantly in 

 caryophyllaceous plants, keep off" animals which try to climb up the stem to reach 



