164 



ESSENTIALS OF BOTANY 



aside in a ■warm place, or merely put some pollen in syrup in a watcli 

 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. 



Tulip 1 to 3 per cent. 



Narcissus . . 3 to 5 " 



Cytisus canariensis (called Genista by florists) 1-5 " 



Chinese primrose . . 10 " 



Sweet pea' ... 10 to 15 " 



TropEeolum' 1.5 " 



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 



(^^^kj- the pollen grains adhere (Fig. 1 21). 



1- ^T^^^^^mk Beneath these superficial cells and 



J^^^V running down through the style 



K ' ^^^\ (if there is one) to the ovary is 



J 'iMJ^& \ spongy parenchyma. In some 



A^sfc t^ *iir -^ V pistils the pollen tube proceeds 



^M^;a^' ' ■ through the cell-walls, which it 



^^^» ' f^%'' ' softens by means of a substance 



1^ * which it exudes for that purpose. 



' '" In other cases (Fig. 122) there is 



Fig. 121. Stigma of Thorn- a canal or passage along which 



Ajjple (Datura) with Pol- the pollen tube travels on its way 



len, (Magnified.) to the OVule. 



1 The sweet-pea pollen and that of tropfeolum 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 np 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 

 cover-glass. 



