GENERAL 6 



part way out of the leaf the pupal shell (chrysalis) breaks 

 open on the back, and from it emerges a resplendent little 

 moth, clad in scales of gold and ermine and jet, a veritable 

 atom of Lepidopterous loveliness. 



There is hardly anything in nature more beautiful than 

 are some of the moths that have leaf-mining larvae. 



THE LEAF AS A DWELLING PLACE 



The leaf is a peculiar place in which to live. As every 

 one knows, it is merely an expansion of the plant body con- 

 taining green cells thinly outspread for advantageous ex- 

 posure to the light. A leaf consists essentially of this layer 

 of assimilatory cells, covered by and enclosed in a trans- 

 parent epidermis, and supported by a framework of veins. 

 It is generally, but not always flat, and it varies enormously 

 in details of form, size, structure and content, each species 

 of plant producing leaves after its own kind. We must 

 have the common characteristics of leaves in mind if we 

 would understand the operations of the insects that dwell 

 in them. 



The epidermis is primarily a protective outside layer. It 

 protects the soft semiliquid protoplasmic cells of the par- 

 enchyma from evaporation, and to some extent also from 

 destruction by foraging animals. It consists generally of 

 a single layer of rather thick walled transparent cells, 

 covering the entire leaf and continuous with the epidermis 

 of the stem. It is perforated by pores or stomates that 

 facilitate the intake of carbon dioxide from the air and the 

 outgo of watery vapor. Each stomate is bordered by two 

 guard cells, that automatically regulate transpiration, by 

 opening when moisture is abundant and closing when it is 

 scanty. The guard cells, unlike most other epidermal cells, 

 contain green chlorophyl bodies. Often the cells of this 

 epidermal layer secrete on the outside a common cuticle, 

 that is highly protective and waxy, or varnish-like exuda- 



