56 



THE BREEDING OF PLANTS 



For most farm purposes it is sufficient to grow the intended parents side by side, if they are wind- 

 er insect-pollinated, and let the chance of crossing rest with natural agencies. The seeds are then taken 

 from the most likely parents and sown separately. In the progeny, one may expect to find some plants 

 to his liking or at least such as are suggestive for further experiment. Plants that are 

 freely visited by bees, as the fruit trees, or those in which the sexes are in separate flow- 

 ers, as maize and hemp and chestnuts and melons, are almost certain to be crossed by this 

 method. If the stigma happens to receive pollen from its own flower or plant and also from 

 another plant, the foreign pollen will usually accomplish the fecundation. No doubt 

 a great many of our agricultural varieties have arisen from such natural and appar- 

 ently promiscuous crossing. 



If one wishes to make an exact experiment, however, he must -transfer the 

 pollen himself under conditions of control, both to ensure that crossing takes place 

 and that the pollen is from a given parent. The manual operation of crossing is of 

 four parts : (1) protecting the pistil from undesired pollen ; (2) protecting the pol- 

 len; (3) applying the desired pollen; (4) protecting the ovary and fruit. The operator 

 must flrst be familiar with the parts of the flower. If he has no teacher, he may 

 secure this information from any of the school botanies ; and Figs. 14 to 

 17 and 76 will aid him. In the succeeding pages he will find the flowers 

 of the different crops displayed. 



(1) Protecting the stigma. — If the flower contains stamens, the anthers must 

 be removed before pollen is discharged. The discharge is likely to take place 

 about as soon as the flower opens. The pistil must also be protected from foreign 

 pollen. This means that the pistil must never be exposed to wind or insects. The 

 protecting of the the pistil, then, is of two kinds, — removing the anthers (emascu- 

 lation), covering the flower. Usually the bud is opened just 

 before it is ready to burst, the anthers clipped off or broken off, 

 and the flower covered securely with a thin paper or muslin bag. 



(2) Protecting the pollen. — In the meantime the pollen- 

 bearer has been looked after. It is safest to cover with a bag 

 the flower or cluster of flowers from which pollen is 

 to be taken, for insects may leave foreign pollen on the 

 anthers. This precaution is not often taken, however, 

 for the operator is careful to take his pollen only from 

 unopened anthers. In some cases the pollen ripens in 

 advance of the pistil, or it must be secured from a dis- 

 tance. It will usually retain vitality a few days if 

 carefully dried (not heated) and kept dry in an envel- 

 ope. Some species have short-lived pollen, and some 

 have relatively long-lived pollen : it should be the aim 

 to have it as fresh as possible, when applied to the 

 stigma. 



(3) Applying the pollen. — Usually the stigma is not 

 ripe or "receptive" when the flower is emasculated. 

 The flower is to remain covered, therefore, until the^ 

 stigma is receptive. This epoch is determined by the 

 looks of the stigma, a point to be accurately deter- 

 mined only by experience. The ripe stigma usually 

 exudes a sticky or glistening covering, or it becomes 



rough and papillary. A hand lens will aid greatly in determining the proper 

 time. A fresh ripe anther is crushed (if the pollen is taken fresh from the 



flower) on a knife-blade or thumb-nail, and some of the liberated pollen applied to the stigma by means 

 of a needle-point or other small implement. The stigma is completely covered if possible. Then the bag 

 is replaced. 



(4) Protecting the forming fruit. — The bag is allowed to remain a few days, until all danger of 

 further fecundation is removed. It is usually replaced by a mosquito-netting or tarlatan bag, in order to 

 protect the fruit from insects or mechanical injury. This bag also aids in locating the fruit amongst 



Fig. 76. 

 Flowers (of funMa or day 

 lily) in various stages 

 of development. The 

 open flowers show the 

 stamens, 8, and pis- 

 tils, p. The large bads 

 above these are in the 

 proper stage to be 

 opened and emascu- 

 lated. It is well to 

 emasculate all the buds 

 that are mature 

 enough; the remaining 

 buds and any open 

 flowers are removed, 

 and the emasculated 

 ones covered with a 

 bag. 



Fig. 77. Crossed flowers pro- 

 tected by a paper bag. 



