118 The Rev. P. Keith on the Internal Structure of Plants, 



fine epidermis. This is the simplest mode of vegetable struc- 

 ture, as has been observed by M. Mirbel in his Anatomy of 

 Plants. It may be exemplified in a variety of species belong- 

 ing to the class Cryptogamia, particularly in the orders Algcc 

 and Fungi. In the Alga you have a good example of it in 

 Tremella arborea, which presents, upon external inspection, 

 the appearance of a sort of irregular mass of wrinkled pulp 

 or jelly, of a brown or reddish colour, adhering to the surface 

 of rotten timber or trunks of decayed trees, without any visible 

 root, and without the appendage of either branch, or leaf, or 

 of conspicuous flower or fruit. If you cut it open it still pre- 

 sents to you merely the appearance of a mass of pulp, or of 

 parenchyma covered with a fine epidermis, that is, of a struc- 

 ture wholly cellular. It is well known to many people who 

 are not botanists by the name of Witches' Butter. In Tre- 

 mella Nostoc you have an equally good example, as also in 

 the several species of Clavaria, Sph&ria, Peziza, and many 

 other Fungi. But the subjects of examination should be taken 

 when young, for when they are old they are no longer pulpy. 



The second division comprehends the middle orders of 

 vegetables, that is, orders exhibiting more manifest traces of 

 organization than the foregoing, the caudex being now partly 

 vascular, as consisting of an epidermis that incloses a volu- 

 minous pulp, interspersed with bundles of longitudinal threads 

 or fibres. This mode of structure prevails chiefly in herba- 

 ceous and annual, or biennial plants, and necessarily involves 

 some considerable variety, the pulp being sometimes solid and 

 sometimes tubular, and the fibres being in both cases some- 

 times scattered and sometimes contiguous, sometimes arranged 

 irregularly and sometimes in a determinate order. 



The Pulp solid. — If the stipe of Aspidium Filix-mas is di- 

 vided by a transverse section towards the base, it will be 

 found to consist of an epidermis inclosing a firm and con- 

 sistent pulp, and to exhibit upon the surface of the section 

 five circular spots, of a darker colour than the rest, arranged 

 in a line forming about three fourths of the circumference of 

 a circle, and concentric to the circumference of the stipe. 

 The spots are the divided extremities of five bundles of lon- 

 gitudinal nerves, as may be rendered evident by opening up 

 the stem longitudinally, when the several bundles will appear 

 in the form of strong threads, each surrounded with a proper 

 rind or covering, of a brown colour and membranaceous tex- 

 ture, and extending through the whole length both of the 

 stipe and rachis. 



The Pidp tubular. — If the stem of the Garden Parsnep, 

 Pastinaca sativa, which constitutes externally a fluted column, 



