Description and physiological botany / [J.S. Henslow].

  • John Stevens Henslow
Date:
1839
Catalogue details

Licence: Public Domain Mark

Credit: Description and physiological botany / [J.S. Henslow]. Source: Wellcome Collection.

    280/344 page 266
    PHYSIOLOGICAL BOTANY. PART II. scribed art. gg.; and the interior being an exceedingly delicate homogeneous pellicle. Whatever may be the ultimate determination of botanists, respecting the form- ation and origin of pollen, yet as its grains in a very early stage of their development are free and unattached to the inner walls of the anther, it should seem that from this period at least their growth must depend upon the absorption of nutriment through their surfaces. (262.) Action of Water on Pollen. — If ripe pollen be placed in a drop of water and examined under a microscope, in a few seconds it will be seen to dilate, burst, and violently expel a cloud cf minute granules (Jig. 16O.). These granules are still contained within the inner membrane of the pollen grain protruded through the rup- tured outer membrane, but which is difficult to be observed, on account of its extreme tenuity. It thus forms a sort of rude sack, termed a “ pol- len tube,” and contains a liquid, tbe “ fovilla,” in which are dispersed a number of very minute “ pollen gra- nules.” The outer skin of the grains is ruptured irre- gularly in most Monocotyledons; but in Dicotyledons there are one or more determinate points on its sur- face where a regular dehiscence takes place, and it is through these that the inner membrane then protrudes. In consequence of the effect thus produced on pollen by water, it is liable to injury in rainy seasons and the fer- tility of the seed is often impaired. Although the gra- nules are destined to convey that influence to the ovule which is necessary to secure its fertility, yet their violent expulsion from the grains is not the manner in which this effect is produced. This process constitutes one of the most curious phenomena which have been observed of late years among the many wonders which the micro- scope has brought to light. Considering the minuteness of the objects and the dehcacy of the manipulations re- quisite for these investigations, we must feel surprised
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