SOLANUM TUBEROSUM 519 



form a two-loculed ovary with a single style and stigma. The 

 ovary is superior and the placentation axile. 



The pollen is wind-borne, the flowers produce no nectar and are 

 not visited by insects to any great extent, although Miiller (15) 

 has reported that bumblebees do visit them, obtaining some pollen. 

 It seems probable that in most cases self-fertilization is natural 

 and cross-pollination rare. Several types of sterility exist and East 

 (11) has classified the varieties of potatoes into four groups with 

 reference to this condition : (i) those whose flower buds fall with- 

 out opening; (i) those in which a few flowers open but fall 

 immediately; (3) those in which flowers persist for several days 

 but lack viable pollen; and (4) varieties which flower freely, 

 produce viable pollen, and bear fruits. Differences in environmen- 

 tal conditions may also induce varying degrees of sterility. 



The Fruit. — The fruit is often referred to as a potato "apple," 

 potato "ball," or "seed ball"; and is brown or purplish-green 

 tinged with violet. (Fig. 174, 5.) It is a two-celled, many- 

 seeded berry, about 3^^ inch in diameter, globular to oval in shape, 

 and contains numerous small seeds that are attached to the thick 

 axile placenta and are embedded in the green pulp of the fruit. 

 Single fruits have been known to contain from xoo to 300 seeds; 

 while in other cases no seed at all is produced. 



ANATOMY 



The Seed. — The yellow to yellowish-brown seeds are small, 

 flat, and oval or kidney-shaped. During development, the ovule 

 arises from a massive placenta which is probably cauline, although 

 in later stages the placentation appears to be foliar and axile. 

 The orientation of the ovule is anatropous or partially campy- 

 lotropous. Young (i8) is of the opinion that the ovule does 

 not have the typical anatropous form, since the nucellus and 

 embryo are much curved, and has suggested that it represents 

 a transition stage in the direction of campylotropy. 



A single massive integument develops and there is a long micro- 

 pyle. Soueges (ii) and Bhaduri (5) have investigated the histol- 

 ogy of the integument and are in general agreement. At first 

 the integument is only a few cells in thickness; but, as growth 

 proceeds, it becomes massive and exhibits a definite differentiation 

 of its tissues. Soueges has divided the fully mature integument 

 into three layers: (i) an external region consisting of a single 



