568 THE STRUCTURE OF ECONOMIC PLANTS 



chymatous cells of the placenta which surround their bases. This 

 can be observed within 60 hours after pollination, and the paren- 

 chyma increases until it completely encloses the developing seeds 

 in a homogeneous tissue of thin-walled cells. (Fig. 133, C.) The 

 cells do not unite with the carpellary walls, but press against them 

 and the surfaces of the seeds. At first the tissue is firm and com- 

 pact; but, as the fruit matures, the walls become thinner and the 

 cells partially collapse. Large numbers of round starch grains 

 are included in the gelatinous contents. 



Parthenocarpy. — Parthenocarpy is not uncommon, but the 

 fruits produced are usually small or of poor quality. Hawthorn 

 (14) has reported a case of seedlessness in Texas in a cross between 

 a Large Cherry variety and Bonnie Best. In this instance, the 

 fruits contained seeds in June and usually in July; but were seedless 

 in midsummer, and again bore seed-containing fruits in November. 

 During the seedless period, the plants bore as profusely as at other 

 times and produced fruits of fine quality. 



It is also possible to produce seedless tomatoes experimentally 

 by treating unpollinated flowers with various organic acids. 

 Gustafson (^3) applied organic acids in lanolin to the cut surfaces 

 of the styles of flowers from which the stamens had been removed. 

 Varying results were obtained with different acids, but mature 

 fruits with perfectly normal external appearance were developed 

 in several cases. In the larger fruits, there were occasionally well- 

 developed locules, but the smaller ones did not form them, and in 

 no instance were seeds produced. In general, the pericarp was 

 thinner and the fruits more fleshy, but the water content was 

 approximately the same as in those produced following pollination. 



The Seed. — The mature seeds are oval in outline and very 

 much flattened laterally. (Fig. 197, A.^ They vary considerably 

 in size; and in a random sample of commercial seed averaged 

 3 to 5 mm. in length and i to 4 mm. in breadth. The surface of 

 the buff to straw-colored seed coat is covered with gray or silver 

 hairs and scales which are the remains of the lateral walls of the 

 outermost cell layer of the integument. 



Soueges (30) has described the development of the integument 

 in the tomato and other solanaceous plants, including the manner 

 in which the hairs develop. He divides the massive integument 

 into four regions: an outer or epidermal layer which ultimately 

 produces the hairs, an intermediate parenchymatous region which 



