264 ACTION OF THE POLLEN UPON THE STIGMA. 
pollen-cells to remain in the liquid, they must necessarily burst 
at some point or other, and allow their contents to escape. Under 
these circumstances, as the intine is very extensible, while the 
extine is firm and resisting, it will be found that the former will 
form little projections through the pores or slits of the latter, so 
as to produce little blister-like swellings on its surface (fig. 575). 
Ultimately, however, as absorption of fluid by endosmose still 
goes on, the intine will itself burst and discharge the contents 
of the pollen-cell in the form of a jet (fig. 575). These changes 
will take place more rapidly if a little sulphuric or nitric acid be 
first added to the water. 
When the pollen is thrown upon the stigma in the process 
of pollination (fig. 577, stig), the above described action be- 
comes materially modified. In this case the pollen-cell does not 
Fie.-577. 
x, Wrie..575. Fic. 576. 
Fig. 575. Pollen of the Cherry discharging its fovilla through an opening in 
the intine.——Fig. 576, Trigonal pollen of @nothera with a pollen-tube. 
Fig. 577. Vertical section of the stigma and part of the style of 
Antirrhinum mujus. stig. Stigma, on which two pollen-cells have fallen, 
each of which is provided with a pollen-tube, tp, which is passing through 
the tissue of the style, styl. 
burst, but its intine protrudes through one or more of the pores 
or slits of the extine in the form of a delicate tube (figs. 576 and 
577, tp), which is filled with the fovilla, and called the pollen-tube ; 
this penetrates, as will be afterwards described, through the tissue 
of the stigma (and style ( fig. 577, styl) also, when this is present), 
to the placenta and ovules. This tube is frequently some inches 
in length, and its formation is a true growth, caused by the 
nourishment it derives from the stigma and conducting tissue 
of the style in its passage downwards to the interior of the ovary. 
(See page 271.) 
Professor Duncan has proved that the pollen-tube is not, 
(in all cases at least,) as formerly supposed, a continuous tube, 
that is, having but one cavity ; but that in Tigridia conchiflora 
and other Monocotyledons with long styles which he examined, 
