An Illustrated Flora of the Northern United States, Canada and the British Possessions/Angiospermae
|An Illustrated Flora of the Northern United States,
Canada and the British Possessions
by Nathaniel Lord Britton & Addison Brown
Ovules (macrosporanges) enclosed in a cavity (the ovary) formed by the infolding and uniting of the margins of a modified rudimentary leaf (carpel), or of several such leaves joined together, in which the seeds are ripened. The pollen-grains (microspores) on alighting upon the summit of the carpel (stigma) germinate, sending out a pollen-tube which penetrates its tissue and reaching an ovule enters the orifice of the latter (micropyle), and its tip coming in contact with a germ-cell in the embryo-sac, fertilization is effected. In a few cases the pollen-tube enters the ovule at the chalaza, not at the micropyle.
|Cotyledon one ; stem endogenous.||Sub-class 1. Monocotyledones.|
|Cotyledons almost always two ; stem (with rare exceptions) exogenous.||Sub-class 2. Dicotyledones.|