208 PRACTICAL BOTANY 



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

 (Enothera, Digitalis, &c., or any flower in which the style and 

 stigma are of considerable size. 



III. The style and stigma of flowers of Rhododendron 

 ponticum from which the corolla has already fallen off 

 will also be found to be good material for showing 

 pollen-tubes. Cut transverse sections of the style in 

 the fresh state, mount in dilute glycerine and observe 



1. The tissue of the style with small vascular bundles 

 dotted in it. 



2. The star-shaped central cavity, filled with 

 mucilage, embedded in which may be seen 



3. The small pollen-tubes cut transversely, and 

 embedded in a mass of transparent mucilage. 



Cut longitudinal sections of the same, including the 

 stigma, and mount as before : observe 



1. The irregular stigmatic surface. 



2. The numerous pollen-grains (associated in groups 

 of four) attached to the stigma, and often putting 

 out pollen-tubes which penetrate the tissue of the 

 style. 



3. The pollen-tubes, often to be seen as a dense 

 sheaf, pursuing their course down the cavity of the 

 style : note their thin walls, and the presence of highly 

 refractive plugs, which stop their cavities : look for 

 endings of the tubes, in which the protoplasm will 

 be denser, and one or two nuclei may be observed 

 there. 



IV. Pick out gently a number of ovules from an 

 ovary of a flower of Datura Stramonium, or of Digitalis 

 purpurea, which has just faded, and mount in dilute 

 glycerine. Observe 



