38 



THE GARDENER'S ASSISTANT. 



portant and "natural", inasmuch as, while it 

 expresses one point of difference, it implies many 

 more which are associated with it, but which are 

 not specified. The cotyledons are flat and green 

 and generally of 

 simple conforma- 

 tion (fig. 43). 

 When this is the 

 case, as in the 

 penstemon, they 

 do the work of 

 leaves from the 

 first, and the 

 young seedling 

 can take care of 

 itself from the 

 time when its 

 seed-leaves are 

 unfolded. In 

 other cases the 

 cotyledons re- 

 main under- 

 ground, when 

 they are gener- 

 ally thickened 

 and contain a 

 store of ready- 

 made food -sub- 

 stances UpOIl Fig 43. -Seedling with opposite Cotyledons 

 which the VOUn " ami :lltt ' ru:ite Foliage -leavea {Cytisus 

 •/ O Laburnum). 



plant can feed 



till it is able to supply its requirements by the 

 agency of the leaves (fig. 44). After the coty- 

 ledons the true leaves appear from the sides of 

 the stem and branches. 



Leaf Forms. — Nothing 

 than the form and appear- 

 ance of the leaves in dif- 

 ferent plants, and even on 

 the same plant the differ- 

 ence is sometimes very 

 great. This difference is 

 generally associated with 

 variations in function. If 

 a leaf has to serve the office 

 of protection only, it is 

 then represented by a 

 mere scale, a "leaf-scale", 

 such as is found on the 

 outside of a bud. If its 

 office is to act as a store 

 for water or food -mate- 

 rials, then it is thickened and swollen. If it is 

 to fulfil the complete office of a leaf, then it is 

 broadly expanded to secure exposure to light 

 and air, and its structure and appearance are 



greatly modified according to the circumstances 

 in which the plant is placed. A complete leaf, 

 or, as it is sometimes called, a " foliage-leaf ", 

 has a stalk or petiole, the lower part of which 

 often broadens out into a "sheath", whilst the 

 upper part dilates into a flat plate called the 

 limb or blade. When the leaf-blade emerges 

 from the cortex of the stem or branch without 



:an be more varied 



Fig. 44 —Embryo of Almond 

 with one cotyledon removed. 

 r. Fleshy cotyledon; p, plu- 

 mule ; r, radicle. 



rig. 45. —Pea— Cotyledons opened out. 



Thick cotyledons acting as store-places for food for the use of the 

 embryo-plant during its growth. c,c. The Cotyledons; p, the 

 Plumule or Primary Bud; r, the Radicle. 



the interposition of any stalk, the leaf is said to 

 be sessile. 



The points on the stem or branches whence 

 the leaves emerge are called nodes; if these are 

 close together, the leaves are in tufts or rosettes ; 

 if separated, then the space between any two 

 leaves is called the intemode. The manner in 

 which successive leaves spring from the nodes, 

 of the stem is a point of much importance to be 

 determined. If they spring in succession, the 

 leaves occur at different heights or planes and 

 are then said to be alternate (fig. 43). If two 

 leaves originate at the same time, one on one 

 side of the stem, one 

 on the other, at the 

 same level, they are 

 called opposite (see 

 fig. 34). If more than 

 two spring from the 

 same level, they are 

 said to be whorled or 

 verticillate (fig. 46). 

 So, too, the leaves 

 may be arranged in 

 two, three, four, five, 

 or more vertical rows, and a spiral arrangement 

 may then readily be traced. 



Individual leaves are "spreading", or "ap- 

 pressed" against the stem; erect, deflexed, or 

 bent downwards. The form of the leaf is 

 infinitely varied. Distinct terms are applied 

 to express those differences. These are given 

 in every ordinary text-book. In this place we 

 can only allude to a few of the most important 



Fig. 46 — Oleander— Verticillate 

 Entire heaves. 



