60 



SEEDS AND FRUITS 



em 



B 



65. — A, section through 

 c, embryo; e, endosperm; 



a Potato 

 t, testa. 



In structure these seeds differ from those of the Bean type in 

 that they have three distinct parts, an embryo, endosperm, and 

 seed coat, but in number of cotyledons, which is two, the two 

 types are identical. Since endosperm is present, the seeds of 

 this type are known as albuminous seeds. {Fig. 65.) Although 

 some endosperm is always present, sometimes, however, much 

 of it is absorbed by the embryo during the development of the 

 seed, and in this case the cotyledons, which are comparatively 



free from stored food in 

 many of these seeds, as- 

 sume some importance as 

 storage organs, though not 

 so much as in the Bean 

 type. In the Buckwheat 

 family, represented by 

 Buckwheat, Rhubarb, 

 Docks, and Smart weeds, 

 and also in some plants 

 of the Goosefoot family, 

 the hardened ovary wall, 

 which, when mature re- 

 sembles a seed coat, per- 

 sists as an outer covering over the seed, thus forming with the 

 seed a fruit-like structure known as an achene, a term which is 

 applied to many hard, usually one-seeded fruits, that do not dehisce 

 or, in other words, that do not open to allow the seed to escape. 

 In external characters, seeds of this type present various differ- 

 ences by means of which one can usually identify the family and 

 often the species to which the seed belongs. Those most com- 

 mon in our region range in size from the smallest of the Dodder 

 seeds, which are almost dust fine, to the size of the Castor 

 Bean. The shape, which in many cases is the chief character by 

 which the family and often the species to which the seed belongs 

 is identified, may be globular, oval, flat, or angled. Such colors 

 as red, yellow, brown, and black are common and serve along 

 with shape and size as a means of identifying different seeds. 

 Sometimes the seed coat is much roughened, as in the Cockle, 

 and in some cases, as in the Milkweeds, the seed coat develops 

 hair-like appendages. 



In case of Flax, Buckwheat, Coffee, and the Castor-oil plant. 



B, section through an achene of Buckwheat. 

 em, embryo; e, endosperm; o, ovary wall 

 and testa. Enlarged. 



