Text-book of botany, morphological and physiological . complicated differences indensity. The microspores so far resemblethe macrospores that their exospore has alsoa firm inner layer which is cuticularised andshows an internal structure depending on dif-ference of density. This layer is surroundedin Marsilea by a thick, in Pilularia by athin hyaline envelope capable of swellmg inwater. The Class Rhizocarpeae contains, besidesthe genera that have already been mentioned,only one other, Azolla, which, although notyet accurately known \ is nearly allied to Sal-vinia. The four genera form, therefo
Text-book of botany, morphological and physiological . complicated differences indensity. The microspores so far resemblethe macrospores that their exospore has alsoa firm inner layer which is cuticularised andshows an internal structure depending on dif-ference of density. This layer is surroundedin Marsilea by a thick, in Pilularia by athin hyaline envelope capable of swellmg inwater. The Class Rhizocarpeae contains, besidesthe genera that have already been mentioned,only one other, Azolla, which, although notyet accurately known \ is nearly allied to Sal-vinia. The four genera form, therefore, twogroups ; Sahmiece (Salvinia and Azolla), andMarsilecB (Marsilea and Pilularia); the furthercharacteristics of which need not be furtheralluded to. The Formation of the Tissue of Rhizocarpsis simple in comparison to their externaldifferentiation. An axial fibro-vascular bundlepasses through th^ root, stem, and leaf-stalk,and in the lamina of Marsilea dichotomisesmany times and anastomoses at the is usual in water and marsh plants, the. Fig. 299.—Longitudinal section through the sporeprothallium and embryo o^Marsilea salratrix(\.\t60); am starch-grains of the spore, i inner coatof the spore burst above into lobes, ex the exosporeconsisting of prisms, c the cavity beneath the arclieddiaphragm on which is the basal layer of the pro-thallium, ft the prothallium, wh its root-hairs, a the foot of the embryo, 7u its root, sthe apex of its stem, b its first leaf by which the pro-thallium becomes extended, si the mucilaginous enve-lope of the spores which at first forms the funnel abovethe papilla, and which still envelopes the prothallium50 hours after the dissemination of the spores. parenchymatous fundamental tissue containslarge air-canals placed in a circle as seen in transverse section and separated by radiallamellce of tissue one cell thick. In Salvinia the parenchyma is composed everywhereof lamellae of tissue (Fig. 294 D) w^hich bound th
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectbotany, bookyear1875
