156 ELEMENTS OF BOTANY. 
a bell glass, with a wet cloth or sponge, to prevent evaporation of the 
syrup, and set aside in a warm place, or merely put some pollen in 
syrup in a 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 following 
kinds of pollen form tubes readily in syrups of the strengths indicated : 
ahip'~. : ; ; : ; : ; 1 to 3 per cent. 
Narcissus : : ; , ; : . ds tod Ae 
Cytisus Canariensis (called Genista by florists) 1a. 4% 
Chinese primrose : ‘ : ; : 10 es 
Sweet pea ! : ; : : nee 3 IG tp 1h 
Tropezolum ! : ; : : ; ; fi 
Fic. 141. — Part of Stigma of Thorn 
Fie. 140.— Stigma of Thorn Apple. Vertical section (magni- 
Apple (Datura) with Pollen fied), showing pollen tubes making 
(magnified). their way toward the ovary. 
191. Microscopical Structure of the Stigma and Style. — 
Under a moderate power of the microscope the stigma is seen 
to consist of cells arranged rather loosely over the surface, 
and secreting a moist liquid to which the pollen-grains adhere 
(Fig. 140). Beneath these superficial cells and running down 
1The 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 thinnest 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. 
