FERTILITY 



FERTILIZATION 



579 



or remain to be evaporated. The aim should be to so 

 prepare the land by subdrainage, plowing and surface 

 tillage, and by introducing at least one crop of tap-rooted 

 plants in the rotation, that the surplus water will filter 

 through the soil in a reasonable time. Percolation of 

 rainwater through soils makes them more friable and 

 warmer in spring, aerates the land, promotes beneficial 

 biological and chemical changes, and brings to the soil 

 the nitrogenous compounds contained in the rainwater. 

 Soils which are reasonably porous have the power of 

 retaining more moisture, and of giving it up to plants 

 when needed to a greater extent, than either open sandy 

 or close clay soils do. Fertility, which results in fruit- 

 fulness, is governed very largely by the water and mois- 

 ture conditions of the soil, and these, in turn, are largely 

 governed by the texture of the land and the amount of 

 humus which it contains. 



Legumes, used either as a harvest or cover-crop, pro- 

 mote fertility. A cover-crop of clovers planted August 

 1, and analyzed 64 days after planting, contained of 

 nitrogen, in roots and tops, per acre as follows : 



Tops Hoots Total 



Lbs. Lbs. Lbs. 



Crimson clover 125 30 155 



Red clover 63 40 103 



Mammoth clover 67 78 145 



Clovers and other legumes may be used to fix and store 

 up the uncombined nitrogen of the air and to digest and 

 make available the mineral constituents of the land, 

 thereby greatly increasing the fertility of the soil. 



Barn manures, when properly cared for and intelli- 

 gently applied, not only furnish acceptable plant-food 

 but humus as well. Fertility and high productivity 

 usually may be maintained many years by means of su- 

 perior tillage, leguminous harvest and cover-crops, and 

 the manures of the farm. In some cases a high state of 

 fertility can be maintained only by occasional applica- 

 tions of commercial mineral fertilizers, as phosphates 

 and potash, but too often expensive fertilizers have been 

 substituted for tillage, leguminous plants and barn 

 manures. 



Fertility may frequently be promoted by light appli- 

 cations (20 to 30 bushels per acre) of quick lime. Lime 

 may serve to make plant-food more available, improve 

 soil texture and correct acidity. Its use is especially 

 recommended on clay and moist lands and in orchards 

 where the ground is much shaded. Applications of gyp- 

 sum and salt are sometimes beneficial in maintaining 

 fertility, but they, as well as lime, usually act indirectly, 

 as the soil is seldom deficient 

 in these constituents so far as 

 they are required as plant- 

 food. On high-priced lands, 

 especially those devoted to 

 horticulture, the soil should 

 be made and kept fertile well 

 up to its highest productive 

 power. 



Sometimes soils are rendered 

 unfruitful by the presence of 

 deleterious substances, as or- 

 ganic acids or alkaline salts, 

 or a superabundance of some 

 one or more of its usually use- 

 ful ingredients, as water or 

 nitrogenous matter. An ex- 

 cess of nitrogen stimulates the 

 growth of stalk and straw at 

 the expense of grain, or in the 

 orchard it tends to the for- 

 mation of wood rather than 

 to fruitfulness. The acidity 

 should be corrected by lime, 

 as noted -above, the surplus 

 water removed by drainage, 

 the nitrogenous matter re- 

 duced by the production of 

 such crops as are not harm- 

 fully affected by its super- 

 abundance, such as forage 

 crops which are prized for their foliage rather than for 

 their seeds, while the alkalinity may sometimes be over- 

 come by deep tillage or irrigation. j p ROBERTS 



814. A pollen grain of 

 Lilium Philadelphicum. 

 Before leaving anther, seen 

 in section ; t, the tube 

 cell ; g, the generative 

 cell. The large spherical 

 body in each cell is the 

 nucleus. Magnified 500 

 diameters. 



FEKTILIZATION. The union of two sex-cells, a 

 male cell and a female cell, to form a new one capable 

 of growing into a plant. The term was formerly used 

 to include the transfer of pollen to the stigma (e.g., 

 Darwin's "On the Fertilization of Orchids by Insects"), 

 but this process is now generally distinguished as Pol- 

 lination, which see. In the 

 lower plants, fertilization can 

 be much more readily ob- 

 served than in the seed plants, 

 because in the latter it takes 

 place inside of opaque parts, 

 and therefore can be studied 

 only by the most careful mi- 

 croscopical methods. The 

 process of fertilization is here 

 described as it occurs in lilies. 

 In other seed plants it differs 

 in details. 



The generative cell (g, Fig. 

 814) is produced by the pol- 

 len grain before it leaves the 

 anther. It is usually lenticu- 

 lar, and placed at one end of 

 the grain. Its most important 

 part is the spherical nucleus, 

 which occupies the center. 

 When the pollen grain is con- 

 veyed to the stigma (s, Fig. 

 815), the larger cell (t, Fig. 

 814), nourished by food it ab- 

 sorbs from the stigma, grows, 

 forming a long tube (pt, Fig. 

 815), which traverses the nar- 

 row triangular canal (1, 2, 3, 

 Fig. 815) that leads down the 

 long style to the ovary. In 

 many plants the style is not 

 hollow. In this case, and often 

 when it has a canal, the pollen 

 tube pushes its way between 

 the cells of the style, living 

 on the food it absorbs. About 

 the time the tube begins to 

 grow (or later) the generative 

 cell divides into two. These 

 male cells, or sperms, migrate 

 down the tube (pt, Fig. 815), 

 which makes its way into the 

 opening between the inner in- 

 tegument (i, Fig. 816) of the 

 ovule, penetrates the body of 

 the ovule and enters the em- 

 bryo-sac (K, Fig. 816). Its 

 direction of growth is deter- 

 mined by substances, proba- 

 bly chiefly the sugars, con- 

 tained in the parts which it 

 traverses. 



While the pollen tube has 

 been growing, the female cell 



has been forming in the embryo-sac (E, Fig. 816). 

 The nucleus of this huge cell, originally single, has di- 

 vided into two, these into four, and these into eight 

 nuclei, four migrating to each end. Then one from 

 each group advances toward the middle of the sac and 

 the two fuse into one (e, Fig. 816). One group of three 

 (sometimes after dividing again and again, sometimes 

 only the original three) may organize cells at the antip- 

 odal end of the embryo sac (A, Fig. 816). In the 

 lilies, however, this does not go far, and two of the 

 three antipodal nuclei are seen to be already reduced in 

 size and partially disorganized. They have no further 

 history. The group of three nearest the point of en- 

 trance of pollen tube accumulate the living protoplasm 

 about them and thus organize three naked cells. Two 

 of these (called synergidse) usually begin to disor- 

 ganize before the pollen tube reaches them, but may 

 persist until then or even later. In the lilies they usu- 

 ally disappear early. The third is the egg, or ob'sphere. 

 When the pollen tube enters the embryo-sac, its end be- 

 comes softened and bursts, permitting one or both of 

 the male cells to migrate from it. One male nucleus 



815. Outline of a pistil of 

 Lilium Philadelphicum. 



Cut lengthwise almost 

 through the center ; *, 

 stigma on which pollen 

 grain, p, has been lodged. 

 The course of the pollen 

 tube, pt, is indicated by 

 broken line. At the right, 

 1 , 2, 3, 4, are cross sections 

 of the pistil at the levels 

 indicated by the arrows : 

 1, the stigma; 2, 3, the 

 style, show the triangular 

 canal which leads into the 

 three chambers of 4, the 

 ovary, in each chamber 

 of which are two rows of 

 ovules. Natural size. 



