^-J 



BOTANY OF THE LIVING PLANT 



inwards from the sunn.- of free Oxygen: they are negatively aero- 

 /,,, | ig. 223). If a similar culture be prepared, and a piece of 



J^\±. 



A 



Fig. 222. 



A = Pollen-grains of Corn Cockle (Agrostemma) showing numerous possible points 

 of origin for pollen-tubes, but only one tube, which penetrates at once a papillar cell 

 of the stigma. B = a similar condition in Mallow [Malva), but here numerous 

 small tubes are formed for attachment. (After Strasburger.) ( x 120.) 



the style and stigma of the same species be introduced with the 

 pollen-grains, the tubes curve towards it, and especially towards the 



Fig. 223. 



Pollen grains germinated in a nutritive medium 



under a cover glass, of which the margin is shown 



lne tubes curve away from the margin, that is 



away from the supply ot oxygen. (After Molisch.) ' 



Fig. 224. 



Result of culture of pollen-tubes of 

 Xarcissus Tazetta in neighbourhood of 

 the style and stigma, in 7 per cent, 

 sugar after 16 hours. Diagrammatic. 

 (After Molisch.) ( x 10.) 



surface (Fig. 224). They are positively chemotropic. Their be- 

 haviour on the stigma, where they take a course in close contact 

 with the moist cell-walls, shows that they are also positively hydro- 



