THE EMBRYO. 



325 



embryo is always near to and points towards the micropyle of the 

 seed, viz. to what was the orifice of the ovule ; and if the embryo be 

 straif^ht (as in Fig. 605), or merely partakes of the curvature of 

 the seed, the cotyledons point to the opposite extremity of the seed, 

 that is, to the chalaza. The position of the radicle as respects the 

 hilum varies with the different kind of seed. In the orthotropous 

 form, as in Helianthemum (Fig. GOO) and Buckwheat (Fig. GOG), 

 the radicle necessarily points directly away from the hilum. In the 

 anatropous form, as in the seed of the Lin- 

 den (Fig. 599) and Violet (Fig. G04, 605), 

 the extremity of the radicle is brought to 

 the immediate vicinity of the hilum ; and 

 so it is, although in a different way in 

 the campylotropous seed (Fig. 620, 621) ; while in the amphitro- 

 pous, the radicle points away from the hilum laterally, at a right 

 angle to the funiculus. As the nature of the ovule and seed may 

 usually be ascertained by external inspection, so therefore the situa- 

 tion of the embryo within, and of its parts, may often be inferred 

 without dissection. But the dissection of seeds is not generally a 

 difficult operation. 



639. The position of the embryo as respects the albumen, when 

 that is present, is various. Although more commonly in the axis, it 

 is often excenti-ic, or even external to the albumen, as in all Grasses 

 and cereal Gi-ains (Fig. 622-624), in Polygonum (Fig. 1111), &c. 

 When external or nearly so, and curved circulai'ly around the albu- 



men, as in Goosefoot, Chickweed (Fig. 621), and Mirabilis (Fig. 

 61G), it is said to be peripheric. When bent or folded in such a 



FIG. 620. Campylotropous seed of the common Chickweed (Stellaria media), magnified. 



FIG. 621. Section of the same, showing the embryo coiled around the outside of albumen. 



FIG. 622. Vertical section of a grain of Indian Corn, passing through the embryo : c, the 

 cotyledon ; p, the plumule ; r, the radicle. (A highly magnified portion of the albumen, whicli 

 makes up the principal bulk of the grain, is shown in Fig. 70, p. 54.) 623. Similar section of 

 a grain of Rice. 624. Vertical section of an Oat-grain : a, the albumen ; c, the cotyledon ; p, 

 the plumule ; and r, the radicle of the embryo. 



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