plants. 



The flowers of insect-pollinatca 

 plants, on the other li.n !, :,i. u-iially 

 characterized by beini; -! ■ i l...lll^' 



nectar or fragrance, or i. I i IK ii 



is more or less moist "r i .1,1 it 

 is not easily blown :i".i \ . 1 i i~ 

 attracted to these flow. - i. : . .. v 



colors and the perfuni.. 1 i 1 h 



bespeak the presence ..i \ lii.. 



insect reaches down fur 1 ■,. ■,. . • n. In. Ii 



is near the bottom of ili. il...\.i. - 



parts of its body are aim.. -t ^m. t.. Ii. ...iiji,- 

 dusted with pollen. \\ 1.. n ili. in-.i-i 

 visits another flower soiii.- 1. f tlii^ ]...I1. n 

 may be brushed upon the stigma, and 

 a fresh supply received. This pollen may 

 likewise be carried to another flower, and so 

 on. Thus "cross-pollination, "orthetrans- 

 fer of pollen from the anthers of one 

 flower to the pistil of another, is accom- 

 plished. Many flowers, notably the or- 

 chids, have special modifications of struc- 

 ture apparently developed for the purpose 

 of securing cross-pollination by insects. 

 and preventing self-pollination. The 

 bodies of some insects also have corre- 

 sponding adaptations which insure the 

 cross-pollination of certain flowers which 

 they are in the habit of visiting most fre- 

 quently. This correlation between flowers 

 and their insect visitors has been the sub- 

 ject of extended observ:iti..n " F. rtili-/:t- 



tion of Flowers," by M .'■ M iil.r, 



contains a bibliographx : up 



to 1886. For the distill. I 1 . r- 



tilization and pollinati..ii, il,. :ir:i..lc 



Fertilization, page 579. 



The value of crossim; t.i pl.ini^ \va^ tirsf 

 clearly proved by Charl.^ Haiuin in Is")',!. 



POLLINATION IciSy 



tinued cross-pollination by the 

 st two means, l)ut there is little 

 idence that tlie self-stei-ility now 



i often gerniiuate on the stigma, 

 but fertilizaliun does not take place. 

 The einbrvdlogical reasons for this 

 are not clearly understood. About 

 sixty species of plants are known to be 

 more or less self -sterile. (4) The separa- 

 tion of the sexes in different flowers or on 

 different individuals. It is thought by 

 some that there is a gradual evolution 

 among some kinds of plants toward uni- 

 sexuality, and that adaptations for insect- 

 pollination, dichogamy and self - sterility 

 teps in this process. 



elf-: 



of 



Pollination. 





|)luins, and in gra]M-s. Whenever isolated 

 trees or large blocks of a single variety 

 blossom full, year after year, but drop 

 most of the fruit before it is half-gri>\vn, 

 the trees maybe self -sterile, provided 

 the failure cannot be attributed to fungous 

 disease, insect attack, frost or other in- 

 jury. Familiar examples of self-sterilo 

 varieties are : Wild Goose and Miner 

 plums. Kiefter and Bartlett pears and 

 Esopus Spitzenburg apple. Self-sterility 

 in orchard fruits does not usually result 

 from defectiveness of pollen or pistil, but 

 from a lack of affinity between the two. 

 It is not a constant factor in any variety, 

 but seems to be as easily influenced by the 

 conditions under which the tree is gn^wn 

 as is the size, shape or color of the fruit. 

 The adaptation of a variety to f 



efore, 







do with i 



iftei 



ity. 



Sprengel, Kni-lii. an. I 1 . 1. . \l 

 experiments. 1 1 - i ili 



tinued self-fen; !\ 1 



in inferior oil 1 - 



zation, within ■ ■ _).:,t.r 



vigor to the ..n _ ' ' • ::..n 



between diff. 1 . : .nir 



plant has ii*u;:,,. i... :. |.].i . . ,..i.. an- 



tage. The rea,-..u i..r ilii.-, 1- thai ilie 

 plant resulting from the union of two 

 imlike parents, as in cross-fertilization 

 between flowers on different plants, is 

 more variable than the plant resulting 



from self-fertilization or crossing be- ^ , .w ^, 



tween different flowers on the same plant, »874.^ ^^^^^^^^l ?.„m'=fi!,°"''' 

 and hence has better chance of fitting 

 itself to new conditions. Plants are end- 

 lessly modified to secure cross - fertili- 

 zation and avoid self-fertilization. The 

 principal means by which this end is 

 gained are: (1) Special contrivances in 

 the structure of the flower, which favor 

 cross-pollination. (2) A difference in the 

 time at which the pollen matures and the 

 stigma becomes receptive in the same flow- 

 er (dichogamy). This condition is very 

 noticeable in some varieties of orchard 

 fruits. The prematurity of the pistil is 

 more common than the prematurity of the 

 stamens. (.-)) Self-sterility, which is the 

 inability of a flower to set fruit with its 

 own pollen. It might be expected that, 

 self-sterility would naturally result from 



fruitful by planting near it trees of an- 

 other variety to supply pollen, or by top- 

 grafting part of the tree with cions of 

 another variety. Thus, Miner bears freely 

 if planted with De Soto, and Kieffer with 

 Le Conte. No benefit is derived from 

 planting in an orchard of one variety new 

 trees of the same variety. There are two 

 important points to be considered in tlie 

 choice of a pollinizer. Fir-ct. tli.- two 

 varieties must blus-.m i.,L...ili.r. n.. that 

 cross-pollinatiim liyuin.l ..r iii....l, may 

 take place. Seoon.l, ili.i. i.m.t I... an 

 aflfinity between 111., ix..., -..i!i,i 1 1... |.i-iils 



pollen ot'li;:"."i''i''. '.'..':.. '."i.;..''..'..!d 



fruit. Sueliai. . a . , , . . ...,'. .;..nly 



by experimeiii. In a I . il. . 1 .11 .1 .1 ..f a 

 self-sterile variety wln.'ii is vaiuahie for 

 market, every third or fourth row should 

 be the pollinizer. 

 Orchard Pollination, however, is alarger 



tha 



self- 



orchards have inilieai.l il 

 varieties of orchard fniii . 



sterile or not, will pi... I I., ii.r I'niit 



with pollen other than tli.ir..\\n. 'I'lie 



Baldwin apple will usually I., ar - 1 fruit 



if planted alone, but it will 1. ar Letter 

 fruit it the right variety is plant, .i \v itii it. 

 The probability is that ]ii..~i ..t e.ir 1. a. ling 

 commercial varieties couini.uily planted in 

 large blocks will produce euough better 

 fruit by a judicious intermingling of on« 



