The Various Substances Made by Plants 119 



at least are commonly thus reckoned), so few men possess them. 

 The reason I take to be fundamentally the same in both cases ; — 

 some kinds never get the right start towards constructing them, 

 or else have not the capacity to manufacture them. Chemically 

 the waxes are very closely related to the oils, and no doubt are 

 built up in the same general way. 



Resins. Under this name falls a variety of substances of which 

 typical examples are familiar in the balsam of the Fir and the 

 Pine; in spruce gum; and in rosin; myrrh and frankincense are 

 others; and much of the milky juice (or latex) of plants, from which 

 the rubber of commerce is made, is composed of resins or closely 

 related substances. Chemically the resins are most diverse, and 

 their mode of origin is as little understood as is their function in 

 the plant. They are usually accumulated in special passages, 

 from which they sometimes flow out at a break (e. g., in Pines), 

 in a way to suggest that they serve as a temporary salve, — a kind 

 of first aid to an injury. At times they appear to be utilized as 

 food, which is likely enough, since there is every reason to sup- 

 pose that plants, precisely like animals, when driven by hunger, 

 will resort to the use of materials which they would otherwise re- 

 ject with disdain. 



Glucosides. These substances are more interesting than con- 

 spicuous, the most familiar being that called amygdalin, which 

 gives the bitter taste to seeds of almonds and apples; while the 

 peppery taste, so common in plants of the mustard family, is 

 also due to a glucoside. Their meaning in the plants is not known, 

 although they may find some incidental service in protecting 

 against annuals the parts which possess them. With the gluco- 

 sides belong also some of the brightest coloring matters produced 

 by plants, including the red dye madder and the blue dye indigo. 

 Here also comes erythrophyll (called also anthocyan), that red 

 color with which we have made pleasant acquaintance already as 

 giving brilliant hues to ripened fruits, and the glory to the fo- 

 liage of autumn. Chemically the glucosides owe their name to 



