Whether this explanation can be considered satisfactory must
remain at present doubtful.
There is another remarkable difference between the forms of several heterostyled
species, namely in the anthers of the short-styled flowers, which contain the
larger pollen-grains, being longer than those of the long-styled flowers. This
is the case with Hottonia palustris in the ratio of 100 to 83. With Limnanthemum
Indicum the ratio is as 100 to 70. With the allied Menyanthes the anthers of the
short-styled form are a little and with Villarsia conspicuously larger than
those of the long-styled. With Pulmonaria angustifolia they vary much in size,
but from an average of seven measurements of each kind the ratio is as 100 to
91. In six genera of the Rubiaceae there is a similar difference, either
slightly or well marked. Lastly, in the trimorphic Pontederia the ratio is 100
to 88; the anthers from the longest stamens in the short-styled form being
compared with those from the shortest stamens in the long-styled form. On the
other hand, there is a similar and well-marked difference in the length of the
stamens in the two forms of Forsythia suspensa and of Linum flavum; but in these
two cases the anthers of the short-styled flowers are shorter than those of the
long-styled. The relative size of the anthers was not particularly attended to
in the two forms of the other heterostyled plants, but I believe that they are
generally equal, as is certainly the case with those of the common primrose and
cowslip.
Pages:
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345