[Illustration: FIG. 192.--NARCISSUS OR DAFFODIL. Single flower at the right.] SUGGESTIONS.--=145.= If the pupil has been skillfully conducted through this chapter _by means of careful study of specimens_ rather than as a mere memorizing process, he will be in mood to challenge any flower that he sees and to make an effort to understand it. Flowers are endlessly modified in form; but they can be understood if the pupil looks first for the anthers and ovaries. How may anthers and ovaries always be distinguished? =146.= It is excellent practice to find the flowers in plants that are commonly known by name, and to determine the main points in their structure. What are the flowers in Indian corn? pumpkin or squash? celery? cabbage? potato? pea? tomato? okra? cotton? rhubarb? chestnut? wheat? oats? =147.= Do all forest trees have flowers? Explain. =148.= Name all the monœcious plants you know. Diœcious. =149.= What plants do you know that bloom before the leaves appear? Do any bloom after the leaves fall? =150.= Explain the flowers of marigold, hyacinth, lettuce, clover, asparagus, garden calla, aster, locust, onion, burdock, lily-of-the-valley, crocus, Golden Glow rudbeckia, cowpea. =151.= Define a _flower_. NOTE TO THE TEACHER.--It cannot be urged too often that _the specimens themselves_ be studied. If this chapter becomes a mere recitation on names and definitions, the exercise will be worse than useless. Properly taught by means of the flowers themselves, the names become merely incidental and a part of the pupil’s language, and the subject has living interest. CHAPTER XIX THE FLOWER--FERTILIZATION AND POLLINATION =Fertilization.=--_Seeds result from the union of two elements or parts._ One of these elements is a cell-nucleus of the pollen-grain. The other element is the cell-nucleus of an egg-cell, borne in the ovary. The pollen-grain falls on the stigma (Fig. 193). It absorbs the juices exuded by the stigma, and grows by sending out a tube (Fig. 194). This tube grows downward through the style, absorbing food as it goes, and finally reaches the egg-cell in the interior of an ovule in the ovary (Fig. 195), and =fertilization=, or union of a nucleus of the pollen and the nucleus of the egg-cell in the ovule, takes place. _The ovule and embryo within then develops into a seed._ The growth of the pollen-tube is often spoken of as germination of the pollen, but it is not germination in the sense in which the word is used when speaking of seeds. [Illustration: FIG. 193.--_B_, POLLEN escaping from anther; _A_, pollen germinating on a stigma. Enlarged.] [Illustration: FIG. 194.--A POLLEN-GRAIN AND THE GROWING TUBE.]