. Principes de botanique. La botanique. 98 LES FONCTIONS VÉGÉTATIVES DES PLANTES OE que les deux dernières sont aussi les résultats d'un autre processus de la vie des plantes. 98. "Qu'est-ce que la levure ?-depuis des siècles hommes employés dans les recettes de levure et de brassage sans avoir la moindre idée de ce qu'il est vraiment, ou de la façon dont il provoque la fermentation. C'était parce qu'ils n'ont pas enquêter sur la question. Ce n'est pas avant 1680 que Leeuwenhoek, un ralist natu- néerlandais, ont découvert que la levure liquide contient toujours de petits globules de flottant. C'était 150 ans après ce qu'un scientifique français, Cagniard de la Tour, découvert t

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. Fundamentals of botany. Botany. 98 THE VEGETATIVE FUNCTIONS OE PLANTS that the last two are also the results of another important life-process of plants. 98. "What is Yeast?—For centuries men employed yeast in baking and brewing without having the remotest idea as to what it really is, or of how it causes fermentation. This was because they did not inquire into the matter. It was not until 1680 that Leeuwenhoek, a Dutch natu- ralist, discovered that liquid yeast always contains tiny floating globules. It was 150 years after this that a French scientist, Cagniard de la Tour, discovered that yeast is a living organism, and soon thereafter another observer, Turpin, demonstrated that yeast is really a plant, closely related to the fungi. Thanks to the painstaking work of many other students, and especially of Pasteur, we now have a detailed knowledge of the structure and activity of the yeast plant. It is related to the sac-fungi (Ascomycetes). 99. Microscopic Appearance.—If a drop of yeast mix- ture that has been fermenting vigorously is examined under the microscope, the indi- vidual yeast plants may be readily observed (Fig. 67). They are seen to be unicellular plants, globular or ellipsoidal in form, of various sizes according to age, and devoid of chloro- FiG. 67.—Cells of yeast P^yll. The nucleus can be seen {SaccharomycesSp) Some of only after the cell is stained. the cells are budding. The .3 ^.a.i^J.^.>_.. clear spaces are vacuoles. Many of the larger cells will be seen to have small outgrowths or buds, also of various sizes according to age. It is by the formation of the buds, that is, by budding, that the plant. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Gager, C. Stuart (Charles Stuart), 1872-1943. Philadelphia, P. Blakiston's son & co.

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