. A textbook of botany for colleges and universities ... Botany. 644 ECOLOGY. as is shown by the fact that some of the inner scales are tipped by a minute leaf blade (fig. 1160). When such a bud germinates, the outer scales drop off, while the inner scales progressively assume more and more the characters of foliage leaves, in color and persistence, as well as in shape and size. In Vibtirnum Lentago the bud is protected by two large scales with long attenuated tips, which in spring enlarge at the end into small green blades (figs. 949, 950). Not only do such facts show clearly the essential mo
. A textbook of botany for colleges and universities ... Botany. 644 ECOLOGY. as is shown by the fact that some of the inner scales are tipped by a minute leaf blade (fig. 1160). When such a bud germinates, the outer scales drop off, while the inner scales progressively assume more and more the characters of foliage leaves, in color and persistence, as well as in shape and size. In Vibtirnum Lentago the bud is protected by two large scales with long attenuated tips, which in spring enlarge at the end into small green blades (figs. 949, 950). Not only do such facts show clearly the essential morphological equivalence of foliage leaves and scale leaves, but the identical possibilities of their pri- mordia are capable of experimental demonstration. The removal of the leaves from a pine or lilac shoot while the buds are forming is followed by the development into foliage leaves of primordia that otherwise would become scale leaves, and in most plants the removal of the termi- nal bud during development is followed by the develop- ment into shoots of lateral buds which otherwise would have remained as primordia. Probably, therefore, the stimuli which determine whether primordia develop into bud scales or into foliage leaves are external, but the pre- cise factors involved are unknown. Among the features of buds most in need of explanation are these: the arrest of the shoot primordia at a certain definite stage in development, apparently without external inhibitory influence; the failure of the external leaf primordia to develop into foliage leaves; and the development in unusual thickness of cutin or cork layers on the ex- posed under surfaces of the scale leaves. Experiment has thrown some light on the cause of arrested shoot development, as will appear elsewhere (p. 735), but why leaf primordia that apparently are exposed to favorable conditions fail to reach their developmental possibilities remains to be explained. Nor is it understood why scales develop cutin in suc
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
