. Manuel de botanique. La botanique. 56 Manuel de botanique nous avons déjà étudié ; ils partent de l'hori- zontal branches à peu près à la même place à laquelle les groupes de branches vers le bas, mais ils commencent à se développer dans l'air. Après un de ces branches verticale a augmenté pour un temps, son extrémité supérieure commence à gonfler, formant un corps globulaire qui deviendra un sac de spores (Fig. 22, c). Lorsque le sac de spore a atteint près de sa pleine taille, un mur en forme de dôme est formé en elle, le divisant en une partie centrale et une partie extérieure. Le protoplasme (y compris les noyaux et cytoplasme) qui remplit l'e

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. Textbook of botany. Botany. 56 TEXTBOOK OF BOTANY branches we have already studied; they start from the hori- zontal branches at about the same places at which the groups of downward branches start, but they grow upward into the air. After one of these upright branches has grown for a time, its upper end begins to swell, forming a globular body that will become a spore sac (Fig. 22, c). When the spore sac has reached nearly its full size, a dome-shaped wall is formed in it, dividing it into a central portion and an outer portion. The protoplasm (including cytoplasm and nuclei) which fills the outer portion of the spore sac now cuts itself up into a large number of small cells (Fig. 22, d). When the spores are ripe, the outer wall of the spore sac breaks (Fig. 22, e, /), and the spores are scattered. If a spore falls upon moist bread or some other substance on which the mold can live, it begins to grow into a new plant. The spores are so light that they are easily carried about by currents of air. Like the spores of bacteria and of yeasts, they are present in the air practically everywhere that human beings live, and this is why Rhizopus nearly always appears on moist bread that is exposed to the air. 82. Germination of the Spores.—A mold spore can live for some time in a dry place without germinating. But if it falls in a place favorable for growth, it soon develops into a new plant. Germination begins with the appearance of a swelling at one side of the spore (Fig. 23, 5); this swelling grows longer and begins to look like a branch of a mature plant. Sometimes two or more outgrowths. Fig. 23. — A, a ripe spore of the bread mold, much enlarged. B, C, D, stages in the development of spores into young plants.. 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.. Allen, Charles E. (Charles Elmer), b.

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