164 ELEMENTS OF BOTANY 
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 possi- 
ble, using syrups of various strengths. The following kinds of pollen 
form tubes readily in syrups of the strengths indicated. 
alipviss oe es tp Ge A Ae ee to 8 percent, 
ENGTCISSUS EN pon a eee i een oe cee 3 to 5 « 
Cytisus canariensis (called Genista by florists) 15 “ 
(Chimése primrose... ce oe ce Go eS 10 “ 
Sweetupeas =o: ae 2 ee Re ay ee OOM 
Tropeolumitis. aoe «2 ao) Ge ck a ee 15.) 
192. 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. 121). 
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. 122) there is 
Fic. 121. Stigma of Thorn- a canal or passage along which 
Apple (Datura) with Pol- the pollen tube travels on its way 
len. (Magnified.) i 
to the ovule. 
1 The sweet-pea pollen and that of tropwolum are easier to manage than 
any other kinds of which the author has personal knowledge. Hf 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 forma- 
tion of pollen tubes often proceeds most rapidly just inside the margin of the 
zover-glass. 
