STUDIES OF SEED-PLANTS 221 



the oil of lemon from which lemon extract is made. Notice that this 

 oil is very volatile and soon evaporates. It can be collected and 

 preserved by dissolving it in strong alcohol, making lemon-extract. 

 If a portion of the white part of the rind is removed and very thin 

 cross sections are made, it will be seen to consist of layers of cells 

 very much like the corky layer of the potato skin. What is the 

 function of this layer? 



Cut transversely across the middle of a lemon. Note number 

 and shape of cavities. What relation exists between the number 

 of seed-cavities and the number of knobs left in the depression after 

 removing the calyx ? The cavities are entirely filled with a pulpy 

 mass consisting of little irregular-shaped tubes or bags containing 

 the juice. Make sections at various levels until you find seeds; 

 then observe their arrangement. 



The gooseberry and cranberry are simple fleshy fruits 

 similar to lemon and tomato. 



Bananas, navel-oranges, and seedless grapes are cultivated 

 varieties in which ovules do not develop into seeds, but the 

 ovary-wall becomes a fleshy fruit as in natural seeded 

 varieties. 



The pineapple and mulberry are aggregates of fleshy fruits 

 formed from numerous flowers crowded on a short flower-stalk, 

 which remains in the center of the ripened mass. They are 

 called multiple fruits. 



215. Stone-fruits. Peach, plum, cherry, and apricot. 

 Each of these so-called " stone-fruits " contains a hard stone- 

 like body near the center of the edible fleshy mass, and the 

 whole is inclosed in a thin, tough skin. In these fruits, the 

 inner part of the wall of the ovary develops into a hard, stony 

 substance inclosing the seed and the outer part of the ovary- 

 wall forms a pulpy edible tissue. Inside each " stone " or 

 " pit " is a true seed (often called the kernel) with its own 

 seed-coat. This kernel corresponds to a date seed, but 

 the ovary-wall of the date forms fleshy substance close around 

 the seed and no hard stony shell as in the peach and the plum. 



The walnuts and hickory-nuts are similar to stone-fruits, 

 except that their outer fleshy part gets hard late in the sum- 



