16 



PRACTICAL COURSE IN BOTANY 



seeds by a slight roughness, is the chalaza, or organic base of 

 the seed, where the parts all come together like the parts of a 

 flower at their insertion on the stem. Where was it situated 

 in the common bean? How does this differ from its 

 position in the castor bean ? Where the rhaphe ends, 

 just at the beak of the caruncle, you will find the hilum. 

 The micropyle is covered by the caruncle, which is an 

 outgrowth around it. 



Now cut a vertical section through a seed that has been 

 soaked for several days, at right angles to the broad sides, 

 and sketch it. Label the white, pasty mass within the 

 seed coats, endosperm. Can you make out what the narrow 

 white line running through the center of the endosperm, divid- 

 ing it into two halves, represents? Make a similar sketch 



of a cross section. 

 Notice the same 

 white line running 

 horizontally across 

 the endosperm, di- 

 viding it into two 

 equal parts. To 

 find out what these 

 lines are, take an- 

 other seed (always 

 use soaked seeds for 

 dissection) and remove the coats without injuring the kernel. 

 Split the kernel carefully round the edges, remove half the 

 endosperm , and sketch the other half with the delicate em- 

 bryo lying on its inner face. You will have no difficulty 

 now in recognizing the linos in your drawings as sections of 

 the thin cotyledons. Where is the hypocotyl, and which way 

 does its base point ? Remove the embryo from the endosperm, 

 separate the cotyledons with a pin, hold them up to the light, 

 and observe their beautiful texture. Sketch them under the 

 lens, showing the delicate venation. Is there any plumule ? 

 Test the endosperm with a little iodine. Does it give a 



Figs. 20-22.— Castor bean (slightly magnified) ; 20, 

 back \'iew ; 21, front view ; ch, chalaza ; r, rhaphe ; ca, 

 caruncle ; 22, vertical section ;en, endosperm ; cc, cotyle- 

 dons ; hy, hypocotyl ; hi, hilum ; m, micropyle. 



