250 THIRD GROUP. VASCULAR CRYPTOGAMS. 



Histology. Of the forms of tissue in the Ophioglosseae the predominant one is the 

 parenchyma of the fundamental tissue, which in the leaf-stalk especially consists of 

 long, almost cylindrical, thin-walled, succulent cells, with straight transverse walls and 

 large intercellular spaces; these spaces are very large in the lamina of the leaf in 

 Ophioglossum vulgatum, and the tissue is spongy. The epidermal tissue in O. vulgatuin 

 and Botrychium Lunaria has no hypodermal layers ; a well developed epidermis with 

 numerous stomata on both sides of the leaf lies immediately upon the outer layers of 

 the fundamental tissue ; layers of cork are formed at the periphery of the stem, which 

 is completely covered by the scars of the leaves. The vascular bundles in the stem of 

 O. vulgatum, on which the leaves are arranged spirally with a divergence of 2/5, form, 

 according to Hofmeister, a hollow cylindrical network in which each of the meshes 

 corresponds to a leaf. The slender bundles, in number from five to eight, which run 

 through the petiole, unite at its base into a single strand, which descends as the leaf- 

 trace in the stem to nearly as far as the point of entrance of the leaf-trace which is the 

 fifth below it in point of age, and which runs down the stem in the same straight line ; 

 when it has reached this point it joins on to the outside cylindrical network (Holle). In 

 many cases the whole of the tissue which fills the meshes of the network is changed 

 into scalariform vessels, which form a closed hollow cylinder over considerable lengths 

 of the stem ; sometimes the change takes place on one side of the stem only. The 

 leaf- stalk is traversed ,by from five to eight slender bundles arranged in a circle on the 

 transverse section, the fundamental tissue forming wider lacunae between them; on the 

 axile side of each of these bundles is a strong bundle of narrow vessels with reticulately 

 thickened walls, and on their peripheral side is a broad bundle of soft bast (phloem) ; 

 these bundles therefore are collateral, as is usually the case also in the bundles 

 of the skeleton of the stern. The slender bundles branch repeatedly in the lamina of 

 the sterile part of the leaf and anastomose, forming a network with many meshes ; they 

 lie in the mesophyll which contains chlorophyll and do not form projecting veins. The 

 four vascular bundles which traverse the leaf-petiole of Botrychium Lunaria are 

 concentric. Each of them consists of a broad axile band of- scalariform or reticulate 

 tracheides surrounded by a thick formation of phloem, which shows an inner layer of 

 narrow cambiform cells, while the outside is formed of thick-walled, soft, bast-like 

 prosenchyma, as in Pteris and other Ferns. The bundles form repeated bifurcations 

 in the lobes of the sterile lamina, and run through the middle of the mesophyll without 

 fonning projecting veins. The fundamental tissue forms no bundle-sheath round the 

 vascular bundles of the leaves in Ophioglossum ; in Botrychium the sheath is only 

 slightly different from the surrounding parenchyma, being distinguished only by the 

 undulation of the longitudinal band in the middle of the radial side-walls of the cells. 

 Russow states that the vascular bundle-system in the stem of Botrychium manifests a 

 slight subsequent growth in thickness *. 



It was stated above on the authority of Holle that a root arises normally beneath 

 each leaf ; the leaf-trace after passing down the central cylinder bends out into the root. 



Habit and Mode of Life. The number of leaves which make their appearance 

 each year is small and constant in each species ; thus Ophioglossum vulgatum and 

 Botrychium Lunaria unfold a single leaf only each year, B. rutaefolium two, a sterile 

 and a fertile one, O. pcdunculosum from two to four, as Mettenius informs us. The 

 development of the leaves is extraordinarily slow ; in Botrychium each leaf requires 

 four years, the first three of which it spends under the ground ; the two branches, the 

 sterile and the fertile laminae, are commenced in the second year, and are further 

 developed in the third, but do not appear above the ground till the fourth (Fig. 202) ; 

 this recalls the slow growth of the leaves of Pteris aquilina ; the case is the same with 

 Ophioglossum vulgatum ; in both genera the sporangia are commenced a full year 

 before they reach maturity. 



1 This is not difficult to verify in older specimens. 



