6o PLANT HYBRIDIZATION BEFORE MENDEL 



the pollen grain by their transparency, and their uncommonly 

 thin and uniform substance. As these plugs or horns gradually 

 arise, one sees also the absorbed water, together with a part of 

 the granular material, press into them and stretch them to burst- 

 ing. They scarcely reach a length amounting to the small diam- 

 eter of the pollen grain, before a slit appears at one side of the 

 base, and in a moment the mixed material, which has already 

 entered the plug, pours forcibly out of the slit, the pollen grain 

 noticeably shrinks together, and the remaining two plugs with- 

 draw almost wholly into the pollen grain, or at least noticeably 

 diminish in size. Sometimes, instead of the three horns or plugs, 

 only two or even only one makes its appearance. The process is 

 similarly described for the pollen grains of Dipsacus fullo?iU7n, 

 Kiiautia orientalis, Linnaea borealis^ as also for species of Gera- 

 nium. Kolreuter accurately describes the germination-pores of the 

 pollen grains as thin places in the coat. If his observations require 

 correction, it is nevertheless well to note their accuracy within 

 their own category, and within the observational limits then pos- 

 sible. 



The third "Fortsetzung" concludes with an extremely careful 

 and interesting natural history account of the sequence of events 

 in the pollination of the stigmas of Hibiscus manihot. 



"At about nine in the morning on a clear, warm day," (of July 1759), 

 he says, "a flower of the species named opened. Its four carmine-red 

 pistils stood upright but close together. The whitish anthers opened 

 gradually, and showed in part their pale, sulphur-yellow and still 

 opaque pollen grains. The knobby dark-red stigmas, which hitherto had 

 remained still quite dry, began, from their long, fine and pointed 

 papillae, to secrete the female moisture, and acquired thereby a glisten- 

 ing, as though they had been painted over with a varnish, or had been 

 saturated with a fine oil. I thereupon placed upon them by means of a 

 delicate brush a limited quantity of the still opaque pollen grains. 

 Soon thereafter these acquired also a glistening appearance, and together 

 with this, a transparency which they had previously not yet had, be- 

 neath their dull appearance. The glistening of the stigmas increased ever 

 more and more, from the moisture which heaped itself upon them ; and 

 the pollen grains borne upon them became, finally, one after the other, 

 so clear and transparent, that the purple-red color of the papillae 

 lying beneath them appeared very plainly through them. During the 

 time, however, when they reached the highest degree of ripeness, they 

 already began to diminish a little in size. Gradually they lost also 

 their transparency again, became ever smaller, and appeared imper- 

 ceptibly to acquire wrinkles. At last they became very small, shrunk 

 gradually together, lost all transparency and dried out. All these changes 

 took place also at the same time with the other pollen grains remaining 



