SPECIAL MORPHOLOGY: FERNS. 193 



and beautiful manner), seldom simply undivided, always flat, and 

 having vascular bundles (nerves, nervi), the ramifications of which 

 are varied and elegant. The leaf is generally connected by a con- 

 tinuous cellular tissue with the stem, on which account the older 

 leaves only wither, to the lower hard part of the leaf-stalk, without 

 falling off. Occasionally, but rarely, a layer of early- withering 

 cellular tissue forms a true articulation (articulatid), so that the 

 leaves become detached from a defined surface (as in Cyathea 

 arbor -ea). Such an articulation (?) never occurs in the continuity of 

 the same leaf, and on this account there are no true folia composita 

 in Ferns. 



Buds are, on the whole, but seldom found in the leaf-axils ; yet 

 they do occur, as, for instance, in the case ofAspidium Filix mas. On 

 this account the stem of Ferns is mostly simple, and always so in 

 the tree kinds. Here, too, a furcate division of the stem at it apex 

 appears to take place without any axillary buds, as in Polypodium 

 ramosum. In the axillary buds, as well as in the terminal bud of 

 the stem, the leaves are rolled together in a spiral manner (circinate 

 aestivation, (Bstivatio circinata).' 



In a few tropical Ferns small hollows occur in the axils of the 

 leaves, at first covered by the epidermis, and filled with a peculiar 

 spongy cellular tissue. Hairs and glands are more rarely met with 

 in Ferns, while, on the contrary, all are more or less covered with 

 small, quickly-withering scales (palece). 



The other extremity of the young plant developes itself down- 

 wards into the earth as a multifariously ramified root, which, as 

 already remarked, soon dies off again in many of the Ferns. 



It frequently happens that individual cells, or groups of cells of 

 a leaf, separate from the individuality of the whole plant, form 

 tubers, and subsequently grow independently into a new plant. 

 These young plants are formed from the leaf-surface, and especially 

 in the angles of the division of the leaf. 



We have some beautiful investigations, as, for instance, those by 

 Kaulfuss*, on the first development of the plant from the spore (fig. 143.) ; 



143 



* Das Wesen der Farnkriiuter, &c., Leipzig, 1827. 



143 Pteris speciosa. a, Germinating spore ; b, early condition of the proembryo 

 c, antheridia. 



