INTRODUCTORY CHAPTER 



the pistil of a flower should not receive its pollen from the stamens 

 in the same flower-cup with itself. Experience teaches that, 

 sometimes, when this happens no seeds result. At other times 

 the seeds appear, but they are less healthy and vigorous than 

 those which are the outcome of cross-fertilization the term 

 used by botanists to describe the quickening of the ovules in one 

 blossom by the pollen from another. 



But perhaps we hardly realize the importance of abundant 

 health and vigor in a plant's offspring. 



Let us suppose that our eyes are so keen as to enable us to 

 note the different seeds which, during one summer, seek to secure 

 a foothold in some few square inches of the sheltered roadside. 

 The neighboring herb Roberts and jewel-weeds discharge 

 catapult fashion several small invaders into the very heart of the 

 little territory. A battalion of silky-tufted seeds from the 

 cracked pods of the milkweed float downward and take lazy 

 possession of the soil, while the heavy rains wash into their im- 

 mediate vicinity those of the violet from the overhanging bank. 

 The hooked fruit of the stick-tight is finally brushed from the 

 hair of some exasperated animal by the jagged branches of the 

 neighboring thicket and is deposited on the disputed ground, 

 while a bird passing just overhead drops earthward the seed of 

 the partridge berry. The ammunition of the witch-hazel, too, 

 is shot into the midst of this growing colony ; to say nothing of 

 a myriad more little squatters that are wafted or washed or 

 dropped or flung upon this one bit of earth, which is thus trans- 

 formed into a bloodless battle-ground, and which is incapable of 

 yielding nourishment to one-half or one-tenth or even one hun- 

 dredth of these tiny strugglers for life ! 



So, to avoid diminishing the vigor of their progeny by self- 

 fertilization (the reverse of cross-fertilization), various species 

 take various precautions. In one species the pistil is so placed 

 that the pollen of the neighboring stamens cannot reach it. In 

 others one of these two organs ripens before the other, with 

 the result that the contact of the pollen with the stigma of the 

 pistil would be ineffectual. Often the stamens and pistils are 

 in different flowers, sometimes on different plants. But these 



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