294 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



the majority of the AcacicB, Gossypium, Cordia lutea, etc., 

 occur plentifully, sometimes forming thickets. Roughly esti- 

 mated, this zone extends to a height of about 200 feet where 

 it merges into the "Big Tree" zone, in which we find the hand- 

 some Guava tree (Psidium galapageium) , Pisonia Horihunda, 

 and one or two others. Here is a thin covering of soil, small 

 ferns cover the rocks, and the country loses a great deal of its 

 desert aspect. This zone is somewhat ill-defined as to its lower 

 limits. From the "Big Tree" zone, one enters quite abruptly 

 into the "Dark Green" or really humid zone where the soil is 

 rich and the conspicuous vegetation made up in large part of 

 delicate ferns, several species of ConvolvulacecB among the 

 vines, and Scalesia pcdimculata, a tall composite of graceful 

 form. The growth here is really luxuriant, and being com- 

 posed of matted vines and some shrubs (the mass reaching a 

 height of about eight feet), it is nearly impenetrable without 

 the aid of a machete. Every now and then, a pretty little grove 

 of tall Cannas is met with ; going higher up, the Scalesia thins 

 out and the dreary slope presents a rather gloomy appearance. 

 This is a very extensive zone, reaching from 400 or 450 feet to 

 far up the mountain. Above this to the summit, the slope 

 appears equally or more impenetrable, but the color of the 

 above "Brown Zone" suggests lichen-covered trees, taller ferns, 

 with perhaps here and there an open grassy space. Above 400 

 or 500 feet, there is much humidity and the precipitation must 

 be considerable throughout the year. 



The rainy season which lasts from about December to about 

 April, has the effect of making the lower zones fresh and 

 verdant for a short period, and of awakening the insect life 

 which lies dormant there. A little while after the commence- 

 ment of the rainy season (at which time it is a little warmer), 

 insects appear in comparative abundance; and various shrubs 

 and vines support large numbers of Lepidopterous larvae, prin- 

 cipally Sphingidce and NoctuidcB, which though not of many 

 species, are conspicuous by reason of their abundance. At the 

 same time, the enemies of these insects appear. The large 

 greenish Calosomas (Calosoma Hozvardi, Linell), search the 

 bushes diligently for larvae, and do not hesitate to attack and 

 overcome large Sphingid caterpillars. The giant centipedes 



