98 



SEEDS AND SEEDLINGS 



FORMS AND GROWTH OF SEED 



Material. — Various kinds of pods and fruits with the seed still 

 attached to the placentas, such as the following. Straight seeds : 

 buckwheat, smilax, dock, knotweed. Inverted : castor bean, cotton, 

 violet, magnolia, cherry, apple, and the majority of common seeds. 

 Curved : bean, purslane, jimson weed, okra, and most of the pink family. 



130. Straight Seeds. — The most natural, and at the same 

 time the least common mode of attachment is for a seed to 

 stand erect upon its stalk like a pink or a 

 rosebud on its stem. A seed that grows 

 in this manner is said to be orthotropous 

 (Figs. 220, 221). If we 

 imagine the seed coats to 

 be separated from each 

 other and from the em- 



219. — An erect , • ^i. j • 



flower, showing bryos, as m the diagram 



attachment of the (Fig. 220), we shall see 



that the parts all come 



together and coalesce at the base, where 



they are attached to the seed stalk, just 



as all the parts of a flower adhere at 



the receptacle (Fig. 221). This point, 



the orgaijic base of the of junction of these 

 seed, is the chalaza, and 

 you can now understand the tendency of 

 the coats of the different seeds examined 

 to cohere there. An inspection of the 

 diagram will show that in orthotropous 

 seeds the hilum and chalaza will always 

 coincide. At the other end, the tip or 

 apex of the seed (Fig. 220), the coats do 

 not quite come together, thus causing the 

 small aperture that we labeled "micropyle" 

 in our drawings. In this arrangement 



parts at base {after ^^ micropyle will always be opposite the 

 chalaza, and it marks the organic apex 



of the seed as the chalaza does its base. 



220. — Diagrammatic 

 section of a typical 

 or orthotropous seed 

 (Gray), showing the 

 outer coat, a\ the in- 

 ner, b ; the nucleus, c ; 

 the chalaza, or place 



221. — Section of 

 an upright flower, 

 showing insertion of 



