SEX ASTD FERTILIZATION. 105 



determined by dissecting the stigma and style at vari- 

 ous stages of the growth of the pollen tubes. 



Prof. Sachs, in referring to the fertilization of seeds, 

 says: " Sijice every ovule requires^Qn^^oJJ^i^tuJ^ for its 

 fertilization, the number of tubes. vyTnch outer the ovary 

 depends, speaking generally, 011 the number of the 

 ovules" contained in it ; the number of pollen tubes is, 

 however, usually larger than that of the ovules ; where 

 these latter are very numerous, the number of pollen 

 tubes is therefore also very large, as in the Orchideae, 

 where they may be detected in the ovary, even by the 

 naked eye, as a shining, white, silky bundle. " 



\yhile it is no doubt true that each ovule must except 

 in rare instances come in contact with a pollen tube in 

 order to be fertilized, it is not at all necessary or prob- 

 able that a distinct and separate tj^jbe or filament starts 

 from the pollen on the ctigma, thence passing through 

 the style to eaclJ ovule to be fertilized, especially in those 

 plants .where there are many seeds produced in a seed- 

 vessel,, as in the Lilies, Mallows, etc. But instead of the 

 multiplicity of pollen tubes that would be required if 

 one was formed for each ovule, several ovules .become 

 attached to the side otone pollen tube as it passes length- 

 wise through the carpels. As the seed grows or enlarges 

 the little branch of the tube can be readily seen. Where 

 the pistils correspond in number with the cells in the 

 seed-pod, as in the Abutilons, one pollen tube suffices for 

 the fertilization of the two, to six or more ovules in each of 

 the eight to twelve loculicidal cells of our common culti- 

 vated varieties. In some of the Malvaceae, there are a 

 greater number of pistils, or at least branches of the 

 style and stigma, than there are cells of the ovary or 

 even ovules ; consequently, if each stigma produced a 

 pollen tube, they must either coalesce in their growth or 

 some of them become abortive. 



[n such plants as. the Strawberry, Rose and Indian 



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