.1 1 } GENETICS IN RELATION TO AGRICULTURE 



In many species this receptive condition of the stigma is evidenced by the 

 secretion of a viscid fluid on the stigmatic surface. It has been thought 

 that premature pollination wrought disastrous effects on the resulting 

 progeny, but evidence is conflicting on this point. Certain it is that in 

 some species, for example, wheat, no untoward results appear from 

 pollination at the time of castration. Plants with small, entomophilous 

 flowers such as clover and alfalfa may be hybridized by enclosing the 

 insects in a cage surrounding the intended mother plant or plants. 



6. Protection of Pollinated Flowers and Developing Seed. The most 

 commonly used device is the paper bag tied with a string or lead wire 

 or fastened securely with a copper wire label on which the necessary data 

 are written. In many cases ordinary manila bags of suitable size are 

 entirely satisfactory. Where wasps give trouble by cutting holes the use 

 of bags made of ramie fiber will be found more satisfactory since these 

 bags are made with a glossy surface, but even these will give way under 

 the attack of wasps in course of time. Bags made of thin paper which 

 has been treated with oil or paraffine are best for withstanding insect 

 attacks and for use on delicate plants. Many special devices, such as 

 glass or celluloid cylinders plugged with cotton and firmly supported, are 

 used upon occasion. 



Method of Hybridizing Maize. The technique with this plant is 

 simple, but when working among plants growing in close proximity to 

 each other considerable care is necessary in order to prevent accidental 

 crossing. For protection of the pollen manilla or ramie bags, size No. 8, 

 are tied over the top of the plant just as the staminate inflorescence 

 (tassel) is beginning to appear. The female flowers to be crossed must 

 be covered before any of the stigmas (silks) have protruded through the 

 tip of the ear and become exposed. The most satisfactory covering for 

 this purpose is a strong paper bag about the size of the bags used for the 

 tassels. It has been found economical of time to use bags which are 

 folded so that the center line of the bottom is exposed (not "square 

 bottom" bags) and to slit the bottom, fold over once and fasten with a 

 wire clip before covering the ear, with minimum danger of introducing 

 foreign pollen. This device makes it possible to examine the develop- 

 ment of the stigmas. After stripping off the leaf subtending the young 

 ear to be covered the bag is pulled down over the ear as far as possible 

 and tied securely to the stem of the plant. When the stigmas are well de- 

 veloped and while they are still fresh the bag containing the tassel is 

 removed from the intended male parent and carried to the plant which is 

 to be pollinated. A hole is torn in one corner of the bag, the top of the bag 

 covering the ear to be pollinated is then opened, the pollen is dusted over 

 the stigmas and the bag enclosing the ear is closed immediately thereafter 

 and securely fastened. Full data concerning the cross are recorded on. a. 



