178 



Garden and Forest. 



[April io, if 



has shown to be the best adapted to the particular case, the 

 special features of the variety are kept witli very httle, if in- 

 deed any, change. 



Tlie question is still a mooted one, whether such choice 

 varieties do not after a time wear out ? Tlie late Professor 

 Gray was inclined to think that there are differences in this 

 respect ; some varieties appearing to lose a part of their dis- 

 tinctive cliaracters, while others seem to maintain them with 

 no loss whatever. 



The close observer can, by careful selection of the seeds of 

 the varieties of the plants which he has under cultivation, in- 

 tensify nearly any given peculiarity which he wishes to keep. 

 In other words, by selection of the forms which he tiiinks de- 

 sirable, and using in successive seasons the seeds of those 

 varieties only which he wishes to preserve, he can, within cer- 

 tain limits, direct the development of the variation. But there 

 are two very important precautions which must be observed : 

 (i) The pistils of all the flowers on the plants of the desirable 

 variety must be fertilized by the pollen from tiowers of the 

 same plant, and (2) no pollen from other plants must be per- 

 mitted to act on them. By this close-breeding variations can 

 be led along up to a certain point, not always the same for all 

 variedes, but in most cases where care is taken, the diver- 

 gence from the ancestral type can be made very pronounced. 

 It frequently happens that after several generations of this 

 close-breeding the variety acquires the power of taking care 

 of itself and can then come true to seed. 



Now, as a matter of fact, this continuous closa-breeding sel- 

 dom, if indeed ever, occurs in a state of nature. There are a 

 few plants which do not produce seeds to any extent ; for in- 

 stance, the common Horse-radish, the Banana, the Pine-apple 

 and so on, but these have so long been imder cultivation by 

 bud-propagation that the formation of seeds has ceased or, at 

 least, very rarely occurs. But when any variety of plant pro- 

 duces seeds, there is some provision for an occasional break 

 in what might otherwise be uninterrupted close-breeding. As 

 a result of this interruption, the varieties are crossed with 

 others, which serve to check too great specialization. The 

 gross result, then, of all the cross-breeding within the limits 

 of the species is that the average is kept well up to the type of 

 the species. 



The varieties which we should cultivate if we had our own 

 way are by no means those which are adapted to cope with 

 their surroundings, in fact, their very specialization may wholly 

 unfit them for success in the struggle for existence. In a state 

 of nature, the varieties which we might regard as desirable to 

 keep for our own wants are very likely to disappear after two 

 or three generations by simply dropping out of a contest for 

 which they are unfitted. In the majority of cases they are 

 merged by cross-breeding with other varieties, and are thus 

 brought up to the type of the species which, from the nature 

 of the case, represents the form which is best suited to meet 

 all the exigencies of the surroundings. 



In nature, the cross-breeding between varieties of the same 

 species is effected by the agency of the wind, insects, etc., 

 which may carry the pollen of one variety to the pistil of 

 another. The contrivances * for this purpose are among the 

 most wonderful and complicated in organic nature. A com- 

 parison between the results of continuous close-breeding and 

 cross-breeding can be made experimentally. Careful experi- 

 ment must, for honest thinkers, outweigh all speculation and 

 previous conceptions. Such experiments have been conduc- 

 ted by Mr. Darwin in the case of the common plant, Morning- 

 glory, and the results can be readily seen in the following ac- 

 count :t 



"The plants experimented upon in all cases were raised 

 from carefully-ripened seed, and when ready to flower were 

 placed under nets with meshes one-tenth of an inch in diam- 

 eter, in order that all pollen-carrying insects might be excluded. 



" A plant of Ipomcea purpurea (Morning-glory), growing in 

 the green-house, was protected in the manner just described, 

 after ten of its flowers had beep fertiUzed by pollen from their 

 own stamens, and ten others by pollen from a distinct plant of 

 the same species. The seeds from the first ten flowers may 

 be termed self-fertilized, those from the other ten, crossed. 

 The two kinds of seed were placed on damp sand on opposite 

 sides of a glass tumbler covered by a glass plate, with a par- 

 tition between the seeds, and the glass was put in a warm 

 place. As often as a pair of seeds germinated they were put 

 on opposite sides of a pot, with a superficial partidon between 

 them, and the same procedure was followed until five or more 

 seedlings of exactly the same age were planted on the opposite 

 sides of several pots. The soil in the pots in which the plants 



* See Gray's Text-Book, Vol. I., Cross-fertilization, 

 t Gray's Text-Book, Vol. II., page 448. 



grew was well mixed, and the plants on the two sides were 

 always watered at the same time ; thus the seedlings were 

 subjected to practically the same conditions from a very early 

 stage. 



" In the same manner, self-fertilized and crossed seeds were 

 secured during ten generations. The results, so far as these 

 can be shown by measurement of the plants, are exhibited in 

 the following table : 



IPOMOEA PURPUREA. 







Average 





Average 



Ratio between 



Number of 



Number of 



height of 



Number of 



height of 



average heights 



the 



crossed 



crossed 



self-fertil- 



self-fertil- 



of crossed and 



generation. 



plants. 



plants 



ized plants. 



ized plants 



self-fertilized 







in inches. 





in inches. 



plants. 



First 



6 



86. 



6 



65.66 



100:76 



Second . . . 



6 



84.16 



6 



66.33 



100:79 



Third .... 



6 



77-41 



6 



52.83 



100:68 



Fourth . . . 



7 



69.78 



7 



60.14 



100:86 



Fifth 



6 



82.54 



6 



62.33 



100:75 



Sixth 



6 



87.50 



6 



63.16 



100:72 



Seventh . . 



9 



83-94 



9 



68.25 



100:81 



Eighth. . . . 



8 



113.25 



8 



96.65 



100:85 



Ninth 



14 



81.39 



14 



64.07 



100:79 



Tenth .... 



5 



93-70 



5 



50.40 



100:54 



All ten 













genera- 













tions 



Ti 



85.84 



1?, 



66.02 



100:77 



taken 













together. 













The results of close and cross-ferdlization, as shown by the 

 weight of the seed-capsules, are given by Darwin thus : "The 

 offspring of inter-crossed plants of the ninth generation, 

 crossed by a fresh stock, compared with plants of the same 

 stock inter-crossed during ten generations, both sets of plants 

 left uncovered and naturally fertilized, produced capsules by 

 weight as loo to 51." 



Similar experiments by Darwin upon other plants confirmed 

 his experiments related above, and show conclusively the ad- 

 vantage which plants derive from occasional inter-crossing. 

 But the manner in which this advantage to the species may 

 counteract the work of the cultivator, in his improvement of 

 special varieties, appears in its clearest light when we recall 

 what has been said in regard to the diverse directions which 

 variation may take. We can, by constant care, preserve the 

 variations which we choose, but Nature keeps, in the long 

 run, only those which are fitted for the surroundings. 

 Cambridge, Mass. " George Lincoln Goodale. 



Correspondence. 



The Mutilation of Conifers. 

 To the Editor of Garden and Forest : 



Sir. — About 600 feet from my house is a clump of Norway 

 Spruces, some fifty feet high, of vigorous growth [and in per- 

 fect health. During the winter and early spring months the 

 ground under these Spruce is invariably covered with tips and 

 branches from two to twelve inches long. For some years I 

 attributed to squirrels the cutting of these branches, although 

 I have never seen a squirrel on or near the trees. This clump 

 of Spruces is the winter home of several pairs of blue jays, 

 whose screams and noisy demonstrations enliven our neigh- 

 borhood throughout the year. My present belief is that the 

 jay is responsible for the broken tips in this instance. This 

 opinion has been strengthened by the reading of Mrs. Olive 

 Thome Miller's charming little book, " In Nesting Time." 

 Mrs. Miller's patient investigations and her acute observations 

 of the habits of some of our every-day birds are exceedingly 

 valuable. Her account of the eccentric behavior of a pair of 

 blue jays which she sheltered and watched during one winter 

 may help elucidate the present discussion. If your well- 

 informed correspondents who have so admirably discussed 

 the mutilation of Conifers will read pp. 176 to 203 in Mrs. Mil- 

 ler's work they will doubtless conclude that, if the jay be guilt- 

 less of the offense now charged, it is assuredly not from 

 inability on the part of the jay. Should this bird prove to be 

 the culprit, it is to be hoped that horticulturists will spare the 

 jay on account of his many valuable qualities, his beauty and 

 his cheerfulness. J. R. Leeson. 



Boston. 



