92 



SEEDS AND SEEDLINGS 



209, 210. — Dissected cotton seed : 



209, seed with lint removed (magni- 

 fied three times), f, funiculus, or 

 seed stalk, r, rhaphe, ch, chalaza ; 



210, cross section of the seed still 

 more highly magnified, showing the 

 crumpled cotyledons. 



groove on one side, leading from the small end to the big 

 end. Make a sketch of the side showing this line, label 

 it rhaphe, and the point where it begins, at the large end 

 of the seed, chalaza. Look for the hilum at the other 



end of the rhaphe, and for the 

 micropyle near it, at the small 

 end of the seed. If they can 

 not be distinguished on account 

 of the lint, make a longitudinal 

 section of a well-soaked seed 

 and find where the hypocotyl 

 points. Which way did it 

 point in the bean .'' This is the 

 case with all seeds ; the base 

 of the hypocotyl is towards 

 the micropyle, and so we can 

 always tell where the micropyle is by noticing which way 

 the hypocotyl points. Make an enlarged sketch of the 

 section as it appears under the lens, and also of a cross 

 section of another soaked seed about midway between the 

 two ends, showing as accurately as you can the lines of 

 any folds or convolutions that you may see. Label such 

 parts as you can clearly make out, leaving the others till 

 after further examination. 



From a seed that has been boiled for five or ten minutes 

 to soften the contents, gently remove the coats so as to 

 leave the embryo whole. How many seed coats are 

 there .'' How do they differ in color and 

 texture ? Try to distinguish them in 

 the sketches you have made, and label 

 the hard outer one that corresponds 

 to the shell of an egg, testa, the soft 

 inner one, tegmen. What is the use of 

 each .'' As the coats were removed did 

 they seem to adhere to the kernel more tenaciously at 

 one point than elsewhere .? Look for a little dark spot 

 inside near the base, that marks where the seed coats and 

 kernel adhered together. Refer to your sketch of the out- 



211. — Embryo with 

 cotyledons partly un- 

 folded. 



