10 ACADEMIC BOTANY. 



grain is filled with a fluid called Fovilla (L. nourishment). 

 This fovilla (Fig. 4, 3) contains particles which are the 

 equivalents of antherozoids in Cryptogamia; but they 

 have only a slight self-motion. 



20. Parentage. — When the ovule and pollen are mature 

 — at the flowering season — the anther-lobes open and the 

 pollen-grains are set free. Borne by the wind or by in- 

 sects, these grains reach the naked ovule of the Pine, or 

 the stigma of the pistil in the higher phanerogams. Both 

 of these — the Pine ovule and the stigma — have, at the 

 apex, delicate papiUce (L. nipples), which are projections 

 forming what is styled the oondvAing tissue. The pollen- 

 grains fall on this tissue, to which they are held by a viscid 

 fluid it secretes. This fluid acts on the pollen-grain ; if it 

 is a gymnosperm (Pine, Cycas, etc.) its extine bursts irregu- 

 larly (Fig. 48, B) ; if an angiosperm (Grass, Cherry, etc.), 

 its extine is provided with special openings (Fig. 4, 2 to 5) ; 

 through these openings the intine protrudes in the form of 

 a tube (Fig. 3, A, B). This tube contains the fovilla ; and 

 descending through the loose tissues of the style (Fig. 3, A, 

 tp) it penetrates to the embryo-sac, and mingles its contents 

 with the contents of the embryonic vesicle (wiiich is equiv- 

 alent, as we know, to the spore in cryptogamia). The 

 transfer of the fovilla from the pollen-tube to the embry- 

 onic vesicle has never been detected ; botanists suppose it 

 takes place by difiusion through the cell-walls. At any 

 rate, the appearance of the pollen-tube in this neighborhood 

 incites the embryonic vesicle to active work ; and this is 

 called Fertilization also, though not by direct contact as in 

 Vaucheria. The time required for this process varies. In 

 Gymnospernis the pollen-grain remains dormant on the 

 naked ovule for weeks and months before sending down its 

 tube; and the fruit does not ripen until the following year. 

 In the higher plants a much shorter time is required ; some- 

 times a week elapses; sometimes a day; the pollen-tube 

 passes down the long style of the Pretty-by-night {MirahUis) 

 and the Night-blooming Cereus in a few hours. 



