56 BOTANY 



dehiscent fruits the distinction between seed and fruit is always 

 easy. In the indehiscent fruits it is not always so plain, espe- 

 cially in the nuts, grains, and the achene fruits. In all of the 

 above fruits it is necessary to remember that the pericarp, 

 or ovary wall, adheres quite closely to the seed coat. In a 

 grain of wheat the two have actually grown together. In a nut 

 it is always possible to scrape off the seed coat, as a thin 

 brownish covering around the kernel of the nut. Try this with a 

 chestnut. 



Homology of Parts in Flowers and Fruits. — In the acorn, 

 chestnut, and hazelnut a number of leaflike structures come out 

 on the branch just under the fruit and become the capsule of the 

 acorn, the bur of the chestnut, and the husk of the hazelnut 

 respectively. All these structures originate from the same place 

 on the branch. Very early in their growth they appear to be 

 leaflike. We have reason to believe that these structures are en- 

 tirely similar to leaves in structure and position. Any part of a 

 plant or animal that has the same position and structure as an- 

 other similar part on another plant or animal is said to be homolo- 

 gous with it. 



Homology of the Parts of a Flower. — It is believed by botanists 

 that all parts of a flower (sepals, petals, stamens, and carpels) are homolo- 

 gous to each other and also to leaves. It would not 

 take a great stretch of the imagination for you to see 

 how like leaves are the sepals and even the petals of 

 some flowers. 



In roses and in the water lily the petals become 

 thinner as we go inward and become tipped with 

 yellow. On examination, this yellow tip is seen to be 

 Horizontal diagram of a pollen box. In short, the petal has become a sta- 



a lily. The central . i • -^ ^ • i- ^ i i i. 



area represents the men. A very good imitation of a pea pod could be 



ovary; the bean made by folding a pea leaflet along the midrib. In 



shaped structures ^^^ Sedum previously studied it will be seen that the 



the two outer cir- carpels bear the same relation to the stamens as the 



cles the petals and stamens do to the petals. This holds true of petals 

 sepals, respectively. , i t xi. i • a i j. • 



and sepals. In other words, in a flower each part in 



each circle or whorl of parts alternates with the parts of the next succeed- 

 ing whorl. A glance at the diagram will make this more clear. If each 

 of the parts is homologous to leaves, then an opened bud ought to help 

 make this plain. 



