312 THK SEED. 



608. The opposite extreme is an embryo (as in Fig. 686) 

 which appears as a mere speck in the albumen, but in which 

 close microscopical inspection ma}- commonly reveal some differ- 

 entiation, such as a slight notch at one end (that farthest re- 

 moved from the micropyle) of a dicotyledonous embryo, indicating 

 the future cotyledons. Indeed, in Monotropese, Orobanchacese, 

 and some other parasitic dicotyledonous plants, and in Orchids 

 among the monocotyledonous, the embryo is a globular or oblong 

 particle, with no adumbration of organs whatever antecedent to 

 germination. There are all grades between the most rudimen- 

 tary and the most developed embryos. 



609. Under the circumstances of its formation (532), the 

 radicular end of the embr}'o is alwaj's near to and points towards 

 the micropyle of the seed, viz. to what was the orifice of the 

 ovule ; and if the embryo be straight, or merely partakes of the 

 curvature of the seed, the cotyledons point to the opposite 

 extremity, that is, to the chalaza. 



610. The position of the radicle as respects the hilum varies 

 with ttie different kinds of seed. In the orthotropous form, as in 

 Helianthemum (Fig. 664) and Pepper (Fig. 679), the radicle 

 necessarily points directly away from the hilum. 1 In the anatro- 

 pous form, as in Fig. 663, 682, and 684-686, 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. 689, 

 690) ; while in the amphitropous the 

 radicle points away from the hilum later- 

 ally. As the nature of the ovule and seed 

 may usually be ascertained by external inspection, so the situation 



1 Two technical terms, early introduced by Richard to indicate the direc- 

 tion of the radicle (caulicle), or rather its relation to the hilum, are 



Antitropous, when the embryo directs its radicle away from the hilum, as 

 it must in all orthotropous seeds ; 



Orthotropous, also homotropous, when directed to the hilum (more strictly to 

 the micropyle close to the hilum), as in anatropous seeds. These two terms 

 are still employed by many botanists, although superfluous when the ovule 

 or seed is stated to be anatropous or orthotropous, &c. And the term 

 orthotropous, so used, is liable to be confused with orthotropous as applied 

 to the ovule. 



Richard, moreover, termed the embryo amphitropous when curved or coiled, 

 as in duckweed (Fig. 689) and all such campylotropous seeds ; and hetero- 

 tropoiis when neither radicle nor cotyledons point to the hilum, as occurs 

 in the semi-anatropous or amphitropous ovule. Many botanists describe 

 the last by the expression " radicle vague," or, better, " embryo transverse." 



FIG. 689. Campylotropous seed of common duckweed, magnified. 690 Section ol 

 the same, showing the embryo coiled into a ring around the albumen. 



