134 



The Journal of Heredity 







now I EUTILIZATION IS ACCOMPLISIIKU 



This pollen grain has fallen on the stigma and put forth a slender tube wliich 

 will grow down one of the branches of the stigma to the style, through 

 which it will continue to grow until it reaches the ovule. Here, if 

 favored by chance, it will come in contact with the minute ovule or 

 egg cell. The nucleus of the pollen grain {the s])erm cell), which has 

 been gradually slij^jping down the tube, will tlicn enter the ovule, 

 imite with the nucleus of the ovule, and set in motion the machinery 

 of cell division whicli will finally result in the development of a grain 

 of wheat. (Fig. 17j. 



In effecting improvements by cross- 

 breeding the mode of procedure is to 

 cross two varieties of wheat possessing 

 divergent and comi)lemcntary char- 

 acteristics, and selecting from the wideh- 

 varying progeny those ])articular indi- 

 viduals which ])ossess in the liighest 

 degree the specific (|na]ilic'S which wi' 

 are seeking. 



In order to apply such a method 

 effectually it is necessary to have a clear 

 conception of the goal towards which 

 improvement is to be wrought, a knowl- 

 edge of the unit characters of the differ- 

 ent varieties, and of the laws governing 

 the inheritance of these iniit characters. 



The act of crossing, and the actual 

 production of merely new varieties is 

 sim])licity itself — the fixing and i)rodtie- 

 tion of valuable varieties is extremelv 

 difficult. 



Before disctissing the method of cross- 

 ing wheats, let us consider l^riefly the 

 slrnclmx' of a flower of wheat. TIk" 

 "head" or "ear" of whewat is known in 

 botanical langtiage as a spike, and 

 consists of a flattened stem or rachis 

 bearing alternately a series of strtictures 

 known as "s])ikelets." Each "spikelet" 

 or "chest" consists of several flowers. 

 Usually each si)ikelet of most varieties 

 has three to five flowers, from each of 



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