UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 507 



tion. In this case the typical integument is quite suppressed in development 

 and the ovular tissue developed previous to the fertilization stage partakes of the 

 formation of the imperfect seed-coat. . . . 



"From the above we see that the embryo does not require during its develop- 

 ment the accompaniment of the normal development of the ovarial wall and 

 the sporophytic ovular tissue and that the seed-coat alone can develop com- 

 pletely, independent of the formation of the embryo, or of the normal develop- 

 ment of the fruit-wall. But it must be remembered that a nutritive condition 

 which renders the development of the fruit-wall unfavorable may bring about a 

 small amount of embryoless seed. 



"In the process of fruitification the embryo is placed in the first rank for 

 development; if the nutritive condition is favorable, it accompanies the develop- 

 ment of the seed-coat and fruit- wall; if not, only the latter portions are in high 

 degree retarded in development. A similar relation may exist between the 

 fruit- wall and the embryoless seed; under the condition which induces most 

 ovules to develop into embryoless seeds the fruit-wall develops most vigorously; 

 under an insufficient supply of nutritive substances the number- of the seed- 

 forming ovules is diminished, and in this case the fruit-wall is sacrificed for 

 development; in the extreme case of an insufficient nutrition both the fruit-wall 

 and a larger number of ovules are suppressed in development, thereby supplying 

 limited nutritive material to a few ovules, enabling them to form seed. . . . 

 The development of the fruit-wall alone under entire suppression of the ovular 

 development is found in some instances of the habitual parthenocarpy." 



It may be noted in passing that the influences of the nutritive condi- 

 tion of the plant upon fruit setting, fruitfulness and fertility that have 

 been pointed out have been in part upon pistil or pollen abortion and thus 

 more or less indirect and they have been in part direct in apparently 

 affecting the ability of the developing seeds or fruits to complete their 

 maturing processes. No direct or indirect influence on compatibility 

 has been noted. On the other hand, experimental studies with chicory 

 have led to the conclusion that, at least in that species, "self compati- 

 bility and self incompatibility operate independently of the purely 

 nutritive relations of the embryos to their parent plants." ^^^ 



Summary. — The individual plants of many species and likewise many 

 bud-propagated varieties are self unfruitful because their flowers are 

 unisexual and flowers of but one sex occur on a single plant. Among 

 deciduous fruits often self unfruitful from this cause the kaki or Japanese 

 persimmon and the strawberry are the most familiar. Of more general 

 occurrence among fruits is dichogamy. Though seldom complete, 

 it accounts for the failure of many individual blossoms to set fruit and 

 emphasizes the importance of planting with cross pollination in mind, 

 even though the varieties in question are partly self fertile. Heterostyly 

 is not important in limiting the "set" of deciduous fruits. Impotence 

 (partial or complete) resulting from the degeneration of pistils or ovules 

 is very common among certain deciduous fruits. Many varieties, 



