STERILITIES OF WILD AND CULTIVATED POTATOES. 27 
grains is stopped after they are liberated from the tetrad. Breeze (1) 
has 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 variety, 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 m various tuber, fleshy root, bulb, and rhizome-producing 
plants of which mention may be made of the cultivated varieties of the 
gotato, 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 time of Gesner (6, 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 involve 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. 
