306 DR. В. М. SALAMAN ON MALE STERILITY IN POTATOES : 
which in a subsequent generation produce individuals with complete male 
sterility as regards “ quality ” of pollen. 
It was pointed out earlier in this paper that out of 53 plants which all had 
* abundant" and were expected to have fertile pollen, there were two which 
were almost completely sterile—viz. K6.1 and K6.133, i. e. their pollen was 
non-viable. 
Pollen Shapes.—The results of my work in this direction are not altogether 
in accordance with the results of Mr. Sutton (to whom I am very much 
indebted for specimens of wild species and friendly criticism), as recorded in 
his recent paper * on “ Wild Forms and Species of Tuber-bearing Solanum." 
In this paper Mr. Sutton states :—“ The pollen-grains of all wild species аге 
of one particular shape, namely elliptical, whereas the pollen-grains of all 
eultivated potatoes which I have examined are very irregular in form and 
size and very ‘ degenerate.’ ” 
My observations concern the following, viz. :—wild types Solanum verru- 
соѕит, S. tuberosum, S. Maglia, S. etuberosum Lindsay, a number of com- 
mercial potatoes, in addition to about 300 different plants which bave arisen 
out of my research. For purposes of comparison the wild S. nigrum has also 
been examined from time to time. 
Shape of. Grain.—The ** normal " grain is oval or elliptical with truncated 
ends. It is like a partially deflated gas-bag, in which two folds are made on 
either side of a vertical axis, converting a potential sphere into an almost flat 
and nearly rectangular body. 
The irregular grains are sometimes longer than the elliptic, but the majority 
are smaller ; they may be almost any shape, from nearly round to nearly 
oval, but of smaller size than the normal, and from almost square to an 
irregular pebble-shape. Some of the irregular grains are imperfectly or 
incompletely folded grains. 
Hounded grains are found in greatest quantity where the pollen is so 
scanty as to need scraping out of the anther ; they are always covered with 
tags of cellular tissue, and are immature pollen-cells. The circular grains 
are generally opaque and abnormal, but a few will swell and appear as 
healthy as those which were previously oval. "Their protoplasm is, however, 
more coarsely granular, their size smaller, and instead of being colourless 
they have a yellow tint. 
When the water is added all the oval grains at once become circular and 
are seen to be filled out with a finely granular substance, whilst the three 
apertures are at once obvious. 
The irregular grains retain their irregular shape, and are seen to be empty 
or to contain but a small bubble of air. Some few of the imperfectly folded 
grains may swell up into round ones, 
* Journ, Linn, Soc., Bot. vol, xxxviii. 1909, pp. 446-453, 
