. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 152 BOTANY mination of the pollen grain on the stigmatic surface of the flower, enters the ovule in the pollen tube and unites with the egg cell. This process, known as fertilization, is the most important event in the life of the plant, for it is only by means of this process that the ovule is stimulated to become a seed. The fertilized egg grows into the young plant within the seed, known as the embryo see page 34). This method of reproduction, called sexual reproduction, is found in the
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 152 BOTANY mination of the pollen grain on the stigmatic surface of the flower, enters the ovule in the pollen tube and unites with the egg cell. This process, known as fertilization, is the most important event in the life of the plant, for it is only by means of this process that the ovule is stimulated to become a seed. The fertilized egg grows into the young plant within the seed, known as the embryo see page 34). This method of reproduction, called sexual reproduction, is found in the spermatophytes, that is, all seed-producing plants. In the flowerless plants a somewhat similar process takes place. Seeds are not formed, however, but structures called spores repro- duce the plants. Sexual and Asexual Spores. — A spore is usually considered to be a cell which has become dormant, but which will under favor- • able conditions again germinate to form a new plant. A spore, as we shall see, may be formed in one of several ways. If formed by the union of two cells, as is the fertilized egg, it is then said to mold, highly be a sexual spore. If, as is frequently the case, magnified. ^j^^ spore is formed by the separation of a bit of protoplasm from the plant to form a resting cell, then it is called an asexual spore. In most of the so-called " spore plants " both sexual and asexual spores are formed at different times during the life history of the plant. Pteridophytes The Ferns and their Allies. — The fern plants include the true ferns, the horsetails or scouring rushes, and the club mosses. The true ferns are moisture-loving and shade-loving plants; they play an important part in the vegetation of the tropical forests. Many forms are found in the temperate regions; we even have some com- mon ferns that remain green all winter. The ferns are among the most beautiful of our plants, and the study of a common form will amply repay the time so spent. Th
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