FERTILISATION. 131 



FERTILISATION. 



I. Cut median vertical sections through the stigma 

 and upper part of the style of a flower of Datura 

 Stramonium which has just faded. Mount in dilute 

 glycerine, and examine first with a low power. Note 



1. The closely-packed tissue covering the Stigmatic 

 surface, the superficial cells of which are slightly 

 elongated perpendicularly to the surface as hairs. 



2. The more lax Cortical tissue of the style, with 

 numerous intercellular spaces, which appear dark under 

 the microscope. 



3. A central band of more transparent tissue without 

 intercellular spaces (Conducting tissue). 



4. Small vascular bundles, two in number, running 

 up the style ; these may or may not be present in the 

 section, according as it has been cut. 



5. Pollen-grains adhering to the surface of the 

 stigma; from them pollen-tubes, similar to those 

 grown in sugar solutions (cf. p. 127) may often be 

 traced penetrating the tissue of the stigma. 



Now gently boil the sections in the dilute glycerine 

 over a spirit lamp, and examine again. Observe 



1. The Pollen-grains as before. 



2. Pollen-tubes, which may be traced from them 

 through the now more transparent tissues of the style ; 

 they may be recognised by their densely granular 

 contents. 



Other flowers besides the above may be used e.g. species of 

 (Enothera, &c., or any flower in which the style and stigma are of 

 considerable size. 



K 2 



