218 FOUNDATIONS OF BOTANY 



Make a transverse section of the lemon, not more than a fifth of 

 the way down from the stigma end and note : 



(1) The thick skin, pale yeUow near the outside, white within. 



(2) The more or less wedge-shaped divisions containing the juicy 

 pulp of the fruit. These are the matured cells of the ovary ; count 

 these. 



(3) The thin partition between the cells. 



(4) The central column or axis of white pithy tissue. 



(5) The location and attachment of any seeds that may be 

 encountered in the section. 



Make a sketch to illustrate these points, comparing it with 

 Fig. 171. 



Study the section with the magnifying glass and note the little 

 spherical reservoirs near the outer part of the skin, which contain the 

 oil of lemon which gives to lemon peel its characteristic smell and 

 taste. Cut with the razor a thin slice from the surface of a lemon 

 peel, some distance below the section, and at once examine the 

 freshly cut surface with a magnifying glass to see the reservoirs, 

 still containing oil, which, however, soon evaporates. On the cut 

 surface of the pulp (in the original cross-section) note the tubes in 

 which the juice is contained. These tubes are not cells, but their 

 walls are built of cells. Cut a fresh section across the lemon, about 

 midway of its length and sketch it, bringing out the same points 

 which were shown in the previous one. The fact that the number 

 of ovary cells in the fruit corresponds with the number of minute 

 knobs in the depression at its base is due to the fact that these 

 knobs mark the points at which fibro-vascular bundles passed from 

 the peduncle into the cells of the fruit, carrying the sap by which 

 the growth of the latter was maintained. 



Note the toughness and thickness of the seed-coats. Taste the 

 kernel of the seed. 



Cut a very thin slice from the surface of the skin, mount in 

 water, and examine with a medium power of the microscope. 

 Sketch the cellular structure shown and compare it with the sketch 

 of the corky layer of the bark of the potato tuber. 



Of what use to the fruit is a corky layer in the skin? (See Sect. 

 453 for further questions.) 



