18 PART I. — ORGANOGRAPHY. 



Observe the defensive organs of the Gooseberry. Are they all of the same 

 kind or not? Are they modified branches or not ? Examine branches of the 

 Barberry and Hawthorn, and determine the nature of their thorns, whether 

 they are modified leaves or modified branches. 



4. Pull up the following plants by the roots, and examine the underground 

 parts, determining whether they are roots, rhizomes, corms, tubers or bulbs, and 

 give the reasons for your conclusion : Wild or Indian Turnip, Common Blue 

 Violet, Dandelion, Wild Hyacinth, Blood-root and Sweet-flag. Make a careful 

 dissection of an Onion bulb and a Crocus corm, and ascertain how they differ ; 

 also make a careful comparative study of the Sweet-potato and the Irish potato. 



CHAPTER III.— THE LEAF. 



Leaves may be defined as stem-appendages which have their 

 origin just back of the apex of the stem, are regularly arranged 

 upon it, and consist of expansions of its tissues. 



They are never directly borne by roots or by any other 

 organs except the stem. Foliage leaves, which may be taken as 

 the type, are, in the majority of cases, flattened, bilaterally 

 symmetrical, expanded organs, green in color and presenting a 

 distinct upper and under surface. They differ usually from stems 

 by maturing or completing their growth first at the apex, and 

 afterwards at the base, but in Ferns and in some compound- 

 leaved Dicotyledons the basal portion matures first while the 

 apex continues to grow. The primary function of foliage leaves 

 is that of elaborating the plant food. They are pre-eminently 

 the assimilative or digestive organs of the plant. Leaves exist 

 in numerous forms other than that of foliage, and in many 

 instances perform functions altogether different. Several dif- 

 ferent modifications of leaves may often be observed on the 

 same plant. Indeed, there is no organ of the plant body which 

 subserves so many different uses or exists under such a variety 

 of disguises. But, however different their forms and functions 

 may be at maturity, they are alike in the earliest stages of their 

 growth, that is, in the very young bud. At this period of their 

 development, a leaf which is destined to become a spine, a 

 tendril, a stamen or a pistil, cannot be distinguished from one 

 that is to become a foliage leaf. All alike begin as minute 

 papillae or protuberances just back of the growing apex of the 



