FERTILIZATION 207 



colourless styles, curved at their upper ends: the 

 stigmatic surface with its numerous papillose hairs 

 is found on the convex side of the curved part of 

 the style. Note especially the numerous yellow pollen- 

 grains adherent to the stigmatic surface, while it may 

 often be seen that a pollen-tube will proceed from the 

 pollen-grain, and enter the tissue of the style. 



II. 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 sec- 

 tion, according to the direction in which 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. 202), 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 apparent tissues of the style : they 

 may be recognized by their densely granular contents. 



