344 POPULAR SCIENCE MONTHLY. 



simple as possible, because the hybridization is carried on on such a 

 large scale. First the stamens of the flowers to be crossed have to be 

 removed. This is usually done while the flower is in bud and the 

 stamens close together. One circular cut only is sufficient. Care 

 must, of course, be exercised so as not to hurt the pistil. Next protec- 

 tion against insects has to be provided for, as otherwise pollen might 

 be transferred from other flowers and the expected results spoiled. In 

 scientific experiments a great deal of attention is paid to this, and the 

 flowers are carefully enclosed in cases of metal gauze or in especially 

 prepared paper bags, so that no insects can reach them. In practical 

 plant breeding this would, however, be too cumbersome. By the cir- 

 cular cut mentioned not only are the stamens cut through, but the 

 corolla is also removed, and the flowers are consequently not so con- 

 spicuous and do not attract the insects, except where there is fragrance. 

 The majority of Burbank's improved fruit trees belong to the first 

 category. In practical work the visit of a single insect is not so much 

 feared, because all the mischief it may do in bringing the pollen is to 

 produce a valueless hybrid. This can later be destroyed. Besides, 

 the insect may come too late to bring about any result. But there is 

 also a possibility that a new and good hybrid may be produced. The 

 application of any cover is, therefore, entirely out of the question. 

 This is the reason why unexpected results of such practical work are 

 never entirely free from the suspicion that they are due to accidental 

 introduction of pollen. Such results, therefore, do not enable one to 

 draw reliable scientific conclusions. 



Burbank's method is to collect the pollen required for these cross- 

 ings on watch-glasses, as it keeps fresh for about a week. With these 

 glasses he goes to the plants he wants to pollinate and applies with his 

 finger tip a little of the pollen on the stigma. This is, as a rule, not 

 yet ripe, but the pollen adheres to it until it matures. Fecundation 

 thus begins at the time the stigma becomes glutinous, which lessens the 

 possibility of other pollen being introduced. 



I wish now to consider one of the most remarkable features of 

 Burbank's work, the immense scale upon which it is conducted. This 

 is the best plan for obtaining the most variations in a short time. He 

 starts thousands of seedlings for each hybrid, and when the culture 

 admits and the interest requires it, this number is increased to 50,000 

 or 60,000. In order to give an idea of the significance of these figures 

 and of the work they imply, Burbank shows in one of his catalogues an 

 autodafe of hybrid raspberries and blackberries. For the purpose of 

 getting a hybrid with larger berries and bigger bunches he cultivated 

 65,000 seedlings until they blossomed and were in full bearing. A few 

 dozens were selected, and the balance, heavily loaded with fruit, were 

 dug up and gathered in a pile, which was then reduced to ashes. And 



