344 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 
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