Spore

Collier's New Encyclopedia (1921)

the reproductive body in a cryptogam, which differs from a seed in being composed simply of cells and not containing an embryo. Called also sporules. Applied also to the reproductive bodies produced either singly or at the tips of the fruit-bearing threads in fungi. Plants reproduce themselves in two different ways, "vegetatively" or "truly." The vegetative mode of reproduction is merely a continuous growth of parts already formed. It is quite common in nature. Sometimes entire buds separate from the parent plant and produce independent plants. This happens, for example, with some of the buds in the axils of the leaves of Lilium bulbiferum. Sometimes entire pieces of a creeping stem separate from the main stem and begin an independent life. This happens in the case of the strawberry plant. Artificially also a vegetative mode of reproduction is easily brought about. Every one knows how gardeners propagate many species of plants by means of cuttings. As a rule the more lowly the plant the more easy is it to make a successful cutting, and the smaller may the cutting be. Thus, a single leaf or even a small part of leaf of a moss plant, will often, if cut off and placed in a suitable soil, grow into a complete moss plant. In the true mode of reproduction the growth is not continuous. Certain cells of a plant are set apart for this function. These cells are called spores. In plants higher than the Thallophytes, such cells do not grow directly into a plant like that from which they have come, but they give rise to a plant which in its turn, when it reaches maturity, produces cells of two sorts, male and female, which unite with one another, and then from the new cell of dual origin there grows a plant like that from which the spore originally came. Thus, on the under surface of the fronds of ferns there may often be seen many small spore cases. The spores fall to the ground, and produce a little green plant called the prothallium of the fern. The prothallium produces the sex elements. These unite, and from their union grows a new "fern." This indirect mode of reproduction is spoken of as the alternation of generations. In the Thallophytes (algæ, fungi, etc.), the cells which function as spores receive a variety of names, such as telentospores, aredospores, sporidia, stylospores, tetraspores, zoöspores (which are motile), conidia. These names are meant to emphasize some point in their mode of origin and development. In the Bryophytes (liverworts and mosses) and in the P Pteridophytes (ferns, horsetails, etc.), they are always called simply spores. But some of the Pteridophytes (vascular cryptogams), for instance salvinia, produce two kinds of spores, male and female, and hence they are called heterosporous ferns, horsetails, or lycopods as the case may be. In the Spermophytes also (seed plants or phanerogams) the spores are of two kinds. The pollen grains represent the male spores, microspores; and the female spores are contained within the ovule. The sexual generation, the prothallium, which is formed from the spore, loses its character as an independent plant as we ascend the scale of plants from the vascular cryptogams to the phanerogams. In homosporous ferns it lives for a long time; in the heterosporous ferns they, the male and female prothallia, never become entirely separate from the spores, though they burst through the spore cases; in the coniferæ they remain entirely within the spore case. In the phanerogams