94 



SEEDS AND SEEDLINGS 



takes some other name when borne elsewhere than at the 



micropyle, of which 

 it is usually an out- 

 growth. 



Turn the seed over 

 and sketch the other 

 side. Notice the 

 colored line or stripe 

 that runs from the 



212-214. Castor bean (slightly magnified): , , , 



212, back view; 213, front view, cA, chalaza, r, large end to the 



rhaphe, ca, caruncle ; 214, vertical section, e, em- caruncle. This repre- 

 bryo, en, endosperm. 



sents the rhaphe. Its 



starting point near the large end, which is marked in fresh 

 seeds by a slight roughness, is the chalaza. 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 from it. 



Next 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 thick outer coat testa, the deli- 

 cate inner one tegmen, the white, pasty mass within that, 

 endosperm. Can you make out what the narrow white line 

 running through the center of the endosperm, dividing it 

 into two halves, represents ? Make a similar sketch of a 

 cross section. Notice the same white line running hori- 

 zontally across the endosperm, dividing it into two equal 

 parts. To find out what these lines are, take another seed 

 (always use soaked seeds for dissection) and remove the 

 coats without injuring the kernel. Notice the little dark 

 spot where it was joined to the coats at the chalaza. Split 

 the kernel carefully round the edges, remove half the 

 endosperm, and sketch the other half with the delicate 

 embryo lying on its inner face. You will have no diffi- 

 culty now in recognizing the lines 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, 

 and hold them up to the light to see their beautiful texture. 



