308 DR. В. N. SALAMAN ON MALE STERILITY IN POTATOES : 
progressed, yet in the early part the almost complete uniformity of the pure 
oval type coincides with that described by Mr. Sutton. The seedlings when 
examined (see Table IIT.) at varying intervals show the same phenomena of 
degeneration in quality of pollen. 
Amongst the seedlings are some with pollen as good as the parent and 
some as poor in quality as the worst of our domestie varieties. The best 
seedlings, such as Nos. 3 and 45, compare very favourably with the wild 
species examined, and require some careful examination to discover the 
irregular forms, whilst No. 23 and, more especially, No. 24 are composed 
almost entirely of irregular forms. 
These considerations lead one to conclude that the normal shape of dry 
potato-pollen is oval. Irregular grains are either aborted or immature 
grains, and are a measure rather of the male sterility of the variety than 
any indication of varietal or specific difference. The presence of irregular 
grains in the seedlings of etuberosum is no evidence for or against this variety 
being the parent of our domestic potatoes, for such irregularity is present in 
the parent etuberosum as well as in all the wild species examined. 
Conclusions. 
1. The normal pollen-grain of both wild and domesticated potatoes when 
dry is oval. 
2. Irregular grains are immature or dead grains. 
3. The presence of irregular grains 13 not a sign of varietal difference, but 
rather a measure of sterility. 
4. The absence of pollen in the anther is dominant to its presence. 
5. The characters, absence and presence, of pollen segregate in subse- 
quent generations. 
6. The number of living grains in an anther is correlated generally with 
the total quantity of pollen present, but exceptions occur. 
7. Pale heliotrope potato-flowers have always been found to be sterile, and, 
so far as here investigated, heterozygous as regards sterility. 
8. The later in the season the flowers are examined, the more likely is the 
quality of the pollen to deteriorate. 
9. Sterility may arise suddenly in an individual member of a family 
possessing a very high degree of fertility. 
I should like here to express my appreciation of the valuable help that my 
head gardener, Mr. E. Jones, has always rendered me. 
