36 



DR. E. E. GATES— CONTEIBUTI ON TO A 



PL 3. fig. 43, reduced. The three buds to the left of the figure are 0. lata buds as 

 they appear in plants derived from seeds of DeVries. These flowers produce prac- 

 tically no pollen. An account of the pollen development in this form was published 

 in 1907. The phenomena of sterility are very similar to those occurring in hybrids, 

 as Tischler (1908) has also pointed out. The pollen mother-cells or young pollen-grains 

 break down in various stages of development. The tapetal cells disappear early, and 

 the wall-cells of the anther grow into the cavity of the loculus, more or less completely 

 filling it with tissue. This ingrowth of the surrounding cells is doubtless due to the 



release of pressure on their surfaces caused by the disintegration of the tapetal cells and 

 the pollen mother-cells. In some cases it is evident that mitoses of the ingrowing cells 

 have also taken place. The sterility is, therefore, not due to the ingrowth of the tapetal 

 cells, but the pollen mother-cells themselves frequently begin disintegration, from some 



unknown cause at an earlier stage of development. 



The O. lata derived from the Amsterdam cult ares, wherever it is grown, is almost 

 or quite completely sterile in its anthers. This sterility is closely correlated with the 

 shape of the bud. As the illustration (PL 3. fig. 43, three buds to the left) shows, the 

 buds are thick and clumsy, rounded, not squarish, radially asymmetrical, exhibiting a 

 characteristic protrusion, swelling or hernia on one side of the cone near the top. This 

 is in turn due to the crumpling of the petals and their distorted disposition in the bud. 

 It is evident that this irregularity in the development of the petals is closely associated 

 with the failure of pollen development. 



Whatever causes the sterility of the pollen is also concerned in the distortion of the 

 petals, and therefore of the buds, in this characteristic manner. That this is the case is 

 clearly shown by the behaviour of a pollen-producing form of 0. lata^ \^hich is one of 

 many types occurring in a culture of naturalized Oenotheras from Birkenhead, near 

 liverpool, an account of which occurs elsewhere in this paper. This form is probably 

 to be classed as 0. lata, though it differs slightly from H. DeVries's mutant in the 

 characters of the rosette (see PL 4. fig. 44), the leaf-blades being somewhat less crinkled, 

 more elongated and with longer petioles than in typical O. lata^ though the ranges of 

 variability of the two forms appear to overlap in these respects. The individual repre- 

 sented in fig. 42 probably agrees most nearly with DeVries's O. semilata. But the 

 majority of these rosettes agreed more nearly witli O. lata. The flowers, however, were 

 fertile, producing considerable quantities of good pollen, and its buds have nearly or 

 quite the normal squarish shape of other pollen-producing mutants, as shown by the 

 four buds to the right in PL 3. fig. 43, although there remain some traces of the 

 crumpling of the petals seen in typical O. lata. Whether these plants should be 

 classified as O. semilata or as a pollca-producing race of 0. lata is difficult to decide, on 

 account of the variability. MacDougal (1907, p. 16) first mentioned a successful self- 

 pollination of this Liverpool form, supposing it to be an exceptional condition. My 

 1909 culture of 107 plants from one lot of seeds from Birkenhead contained 8 0. lata 

 individuals with the bud-characters just mentioned, all of which produced considerable 

 quantities of pollen, and two others whose place is somewhat doubtful, as they never 



