PLANT BREEDING 343 
present in normal quantity although a certain excess will not be harm- 
ful. If nitrates are present in excess, however, vegetative growth will 
be over stimulated and seed production will be small. A lack of phos- 
phates will produce the same effect upon seed production, but for a 
different reason. Phosphorus is an essential constituent of the proteid 
compounds found in large quantities in the seed. Therefore, if the 
plants are to be in the best condition for crossing, the soil should con- 
tain just the right amount of nitrates for normal growth and a generous 
supply of potash and phosphates. The exact amounts must be deter- 
mined by experience for each soil and each species of plant. 
Other necessary knowledge that can be obtained only front experience 
is which are the best flowers on the plant to serve as parents of the cross 
and what is the proper time for their pollination. For example, in the 
grasses the first flowers that appear usually form larger, healthier seed 
than the later blossoms. In most of the Solanacex, the petunias, browal- 
lias, ete., the exact opposite is true. The time when the individual 
flower is most receptive to pollen is even more narrowly limited. Both 
premature and delayed pollination is the cause of many failures and the 
optimum time should be accurately determined. Having exercised these 
precautions, it remains to study carefully the structure of the flower 
in order that it may be emasculated—i. e., the anthers removed before 
the pollen is shed—with sufficient adroitness that neither the anthers 
shall be opened nor the parts of the pistil injured. Only a few buds 
upon a single flower spike should be operated upon if they are to be 
given the best chance of development. If the buds are very small and 
some pollen unavoidably reaches them, it may be washed off with com- 
parative safety with a dental syringe if done immediately. It is often 
recommended that the calyx and corolla be cut away when emasculating. 
This should be avoided if possible and the floral envelopes left as a 
protection to the pistil. After emasculation the buds should be pro- 
tected from foreign pollen until time for pollination, and again after 
pollination at least until the fruits have begun to form. This protection 
may be an ordinary paper bag when the crossing is done in the field. 
In the greenhouse I find that a square of thin celluloid rolled around 
the flower and caught with two rubber bands, each end being protected 
with absorbent cotton plugs, is a better device. It gives excellent pro- 
tection and allows transpiration. 
But enough of the technique of hybridizing ; the phenomena attend- 
ing it are of more importance. After the pollen is placed upon the 
stigma it begins to grow until it reaches the ovule. Down this tube 
comes the male cell which contains the potentialities of its parent plant. 
This cell fuses with the female cell in the ovule and fertilization is ac- 
complished. From this combination the seed and later the hybrid 
plant results, half of its characters coming from the plant which fur- 
