. Botany of the living plant. Botany; Plants. I-1LICALES leaf-stalk of most modern Ferns (Fig. 374, D). The several strand Dryopteris can be traced into the pinnae and pinnules where they fork freely and end blindly (Fig. 373). But in broad-leaved Ferns such as the Adder's Tongue, and particularly in those of more advan. Fig. 376 a. Dictyostele of the Male Shield Fern dissected out, showing the overlapping leaf-gaps which allow communication between cortex and pith. (After Reinke.) type, such as Onoclea and Woodwardia, a network of veins may arise by their lateral fusion, after the manner of D
. Botany of the living plant. Botany; Plants. I-1LICALES leaf-stalk of most modern Ferns (Fig. 374, D). The several strand Dryopteris can be traced into the pinnae and pinnules where they fork freely and end blindly (Fig. 373). But in broad-leaved Ferns such as the Adder's Tongue, and particularly in those of more advan. Fig. 376 a. Dictyostele of the Male Shield Fern dissected out, showing the overlapping leaf-gaps which allow communication between cortex and pith. (After Reinke.) type, such as Onoclea and Woodwardia, a network of veins may arise by their lateral fusion, after the manner of Dicotyledons (Fig. 46). Both types serve the same purpose, that of supply within the flattened blade ; but the netted venation is functionally the more efficient. Moreover, comparison shows that it is a derivative state, based on an originally forked venation. It thus appears that the vascular system in the leaves of Ferns resembles that of Flowering Plants more nearly than does that of their adult stems. The diversity in vascular structure between the stems of Ferns and those of Seed Plants arises from an essential difference in their way of solving a fundamental problem of support and of supply (see Chapter XXXVI). In the Bracken and Shield Fern the conducting tracts are all of primary origin. They may be traced continuously to their source immediately below the growing point itself, and their outline there corresponds to that which they show when mature. As will be seen in Figs. 376-378, there is no cambium in their make-up. Ferns by their stelar elaborations make the best of this primitive scheme of vascular construction. On the other hand, cambial activity, as described fur Dicotyledons and Gymnosperms in Chapter IV, is an automatic means of meeting the growing demands of increasing size. But it is a morphological afterthought : the tissues it produces being of secondary Please note that these images are extracted from scanned page images that may have been digital
Size: 1068px × 2339px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublis, booksubjectbotany, booksubjectplants
