FERTILIZATION 213 
watch crystal under the bell-glass. Examine from time to time to 
note the appearance of the pollen tubes. Try several kinds of 
pollen if possible, using syrups of various strengths. The follow- 
ing kinds of pollen form tubes readily in syrups of the strengths 
indicated. 
Tulip : ; ; ; : 1 to 5 per cent. 
Narcissus. : > : : , @ to-D? > 
Cytisus canariensis (called Genista by florists) 1S? ee 
Chinese primrose , 2 : ; 16 41," 
Sweet pea } ; ; 2 + SG to Bao 40 
Tropzolum ? . ; ; : : 15 « 
225. Microscopical Structure of the Stigma and Style. 
Under a moderate power of the microscope the stigma is 
seen to consist of cells set irregularly over the surface, 
and secreting a moist liquid to 
which the pollen grains adhere (Fig. 
162). Beneath these superficial cells 
and running down through the style 
(if there is one) to the ovary is 
spongy parenchyma. In some pistils 
the pollen tube proceeds through 
the cell walls, which it softens by 
means of a substance which it exudes 
for that purpose. In other cases 
(Fig. 163) there is a canal or passage, 
Fie. 162.— Stigma of Thorn- 
along which the pollen tube travels Apple (Datura) with Pollen. 
: (Magnified.) 
on its way to the ovule. ; 
1 The sweet-pea pollen and that of Tropzolum are easier to manage than 
any other kinds of which the author has personal knowledge. If a concaved 
slide is not available, the cover-glass may be propped up on bits of the thin- 
nest broken cover-glasses. From presence of air or some other reason, the 
formation of pollen tubes often proceeds most rapidly just inside the margin 
of the cover-glass. 
