SUPPLEMENT 



at any rate, flowers without any intermission. The California holly 

 (Heteromeles arbutifolia] has leaves typical of a dry climate. 



In treating the topic of the protection of plants against the attacks 

 of animals, it is easy to make too sweeping statements. Plants that 

 are poisonous to some animals are eaten with impunity by others, 

 and plants sometimes have an evil reputation in this respect that they 

 do not deserve. But almost any locality furnishes some illustrations 

 of this device for protection. In many parts of the state the poison- 

 ous Datura meteloides, sometimes called "Jimson weed," is common 

 in summer and autumn. The point in teaching this topic is to arouse 

 children's interest in the subject so that they will compare observa- 

 tions, and make inquiries about the supposed poisonous plants in their 

 own neighborhood. A taste and odor that is disagreeable to us may 

 not be equally so to grazing animals or caterpillars. Cows often eat 

 bitter herbs that make their milk utterly unpalatable to us. On the 

 other hand, plants that seem to us quite inoffensive, ferns for instance, 

 seem to be never molested by animals. Hunger often leads animals 

 to devour plants that are so rough and woody as to appear quite safe ; 

 but some of our California dry-season plants seem to have rendered 

 themselves absolutely inedible by these means. We must remember, 

 too, that plants do not need to be absolutely invulnerable to attack. 

 If they can protect themselves against their most common foes they 

 stand a good chance for survival. The turkey-weed {Eremocarpus 

 setigera] is a plant that sheep refuse to eat under the direst necessity, 

 a fact that goes far toward accounting for its prevalence in many 

 parts of California, for sheep have made sad havoc with our native 

 flora. The cactus will be taken up later on, when, it is hoped, the 

 children will have acquired the habit of alertness in discovering 

 plants' devices for protection against animals. 



Plants have various methods of protecting chlorophyll against too 

 much light. In unscreened leaves the chloroplasts group themselves 

 against the sides of the cells in order to avoid intense light. This 

 can be illustrated by fastening dark paper over part of such a leaf on 

 a very bright day; the unilluminated portion of the leaf will be darker, 

 because the chloroplasts are near the upper surface. Desert plants 

 the world over are notably grey, and plants growing in the glaring 

 sand along the sea have the same characteristics in a lesser degree. 

 The fact, that plants do breathe, is given to children without demon- 

 stration, and it is not easy to prove conclusively that dust threatens 

 plants with suffocation. Of course they ma}* find out in a general 

 way that plants do not thrive close to dusty roads, and that house 

 plants need to have the dust washed off their leaves frequently. 



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