STERILITIES OF WILD AND CULTIVATED POTATOES. 27 



f rains is stopped after they are liberated from the tetrad. Breeze (1) 

 as distinguished three conditions of pollen degeneracy in the potato : 



(1) Shriveled and empty pollen grains. In this case deterioration was found to 

 occur after the formation of the pollen mother cell, and rarely before the formation 

 of the tetrads. 



(2) Hypertrophied or swollen grains. 



(3) Absence of pollen grains. In the Up-to-Date A^ariety, in which this condition 

 occurs, apparently normal pollen mother cells were found in very young anthers, 

 but no reduction division was observed. 



In a later paper (Gardeners' Chronicle, ser. 3, v. 73, p. 176 and 188), 

 Breeze reports the presence of minute amoebae in the anthers of Up- 

 to-Date, which she considers may cause degeneration of the pollen 

 mother cells. 



Much has been written regarding the immediate cause of sterilities 

 in cultivated potatoes and a brief summary of this point may be made 

 here. A view most generally advanced is that the conditions of 

 fruitlessness in the potato are due to the high degree to which vegeta- 

 tive reproduction by tubers is developed. Two conceptions have 

 been advanced as to how this relation may operate: (1) That there 

 is direct and immediate correlation either in direct competition for 

 food material or in correlative stimulations resulting in what may 

 be called correlative sterility and (2) that a general degeneration of 

 sex organs frequently results from long-continued cultivation with 

 selection for vegetative vigor, giving a systemic condition which may 

 be called plethoric sterility. 



The idea of correlative sterility due to a direct antagonism between 

 asexual means of propagation and sexual or seed reproduction is an 

 old conception. It has been applied to such cases of sterility as are 

 observed in various tuber, fleshy root, bulb, and rhizome-producing 

 plants of which mention may be made of the cultivated varieties of the 



Sotato, sweet potato, sugar cane, and various species of Lilium and 

 [emerocallis. It has indeed seemed very logical and in harmony with 

 well-recognized phenomena of compensations in growth that vegetative 

 organs which are rapidly storing food may divert and utilize the 

 available food being manufactured in a plant, so that the embryos 

 of the seed are virtually starved to death during development, or 

 perhaps the essential organs of the flowers are so poorly nourished 

 that they are not able to function previous to fertilization. This 

 view has been very generally held since the tune of Gesner (^, p. 53), 

 Medicus (16, p. 202), and Knight {14-, p- 57). It was emphasized by 

 Darwin (2, p. 206, 411) in what he called the "compensation of 

 growth" and by Goebel (7, p. 207), in "quantitative correlation." 

 An excellent statement of this view with reference to the potato has 

 more recently been given by Jones (8). 



That the doctrine of a direct correlative sterility is to be generally 

 applied as thus conceived is now much to be questioned. Bearing 

 on this condition, there are several lines of evidence, all of which 

 point to this conclusion: 



(1) The classical cases of so-called correlative and of plethoric sterility in such 

 plants as the true lilies (Lilium), daylilies (Hemerocallis), and sugar cane are now 

 found to invoh^e such types of sterility as incompatibility and intersexuality. In 

 intersexes fruitfulness is limited to hermaphrodite flowers or to female flowers which 

 are properly pollinated with viable pollen from hermaphrodite or male flowers. Thus 

 clonal varieties of the sugar cane or of the potato which are male sterile are able to 

 produce fruit and seeds in abundance in response to good pollen. 



