The Rev. P. Keith on the Internal Structure of Plants. 113 



and nucleus, or the embryo and its envelopes. The integu- 

 ments of seeds are generally two, but sometimes three or four, 

 distinguished in the nomenclature of the present day by the 

 terms, primine, secundine, tercine, quartine. The exterior 

 integument, or primine, the * testa* of former anatomists, is the 

 original cuticle of the nucleus, not detachable in the early 

 stages of the seed's growth, but detachable at the period of 

 the maturity of the fruit. The integument next in order is 

 the secundine. It originates in the umbilical cord, which, 

 after perforating the testa, or primine, expands either imme- 

 diately, as if from the hilum, or mediately, and from a distinct 

 chalaza, into a multiplicity of ramifications, connected by a fine 

 and delicate membrane that lines the exterior integument, and 

 immediately envelopes the nucleus, unless it should happen to 

 be furnished with a tercine. 



The nucleus, or kernel, is that part of the seed which is 

 contained within the proper integuments, consisting of the al- 

 bumen, with the vitellus, when present, and embryo. 



The albumen is an organ resembling in its unripe state the 

 white of an egg when raw, and in its ripened state the white 

 of an egg when boiled, and forming for the most part the ex- 

 terior portion of the nucleus, but always separable from the 

 interior or remaining portion. In the grasses it forms the 

 principal mass of the nucleus and constitutes the farina of 

 the seed; but in leguminous plants and in the Composite it 

 is not at all to be found, at least as a distinct organ. 



The vitellus, or yelk, where it exists, is an organ of a fleshy 

 but firm contexture interposed between the albumen and 

 embryo, to the former of which it is attached only by adhe- 

 sion, but to the latter by incorporation of substance. There 

 are many tribes of plants in which its presence cannot be de- 

 tected, but it pervades the whole of the extensive family of 

 the grasses, where it assumes the form of a scale on which the 

 embryo rests. 



The embryo, which is 'the last and most essential part of the 

 seed and the final object of the fructification, as being the germ 

 or primordial rudiment of the future plant, is a small, pulpy, 

 and very often minute organ, inclosed, for the most part, 

 within the albumen, and occupying very generally the centre 

 of the seed. It is divisible into two distinct and conspicuous 

 parts, namely, the cotyledon and the plantlet. 



The cotyledon is that portion of the embryo which incloses 

 and protects the plantlet, and springs up during the process 

 of germination into what is usually denominated the seminal 

 leaf, if the lobe is solitary, or seminal leaves if there are more 

 lobes than one. In the former case the seed is said to be 



Third Series. Vol. 5. No. 26. Aug. 1834. Q 



