194 TEANSACTIONS LIVEKPOOL BIOLOGICAL SOCIETY. 



depression and simple pressure on the cover glass may 

 cause the filling up and disappearance of the crease. 



In performing prolonged culture experiments with 

 pollen tubes it is found that the culture medium soon 

 becomes filled with Bacteria, fungal hyphse and Yeast 

 cells and that the development of these organisms injur- 

 iously affects the development and normal growth of the 

 pollen tubes. During the course of the experiments 

 various attempts were made to obtain pure cultures but 

 without success. The effect of adding to the sugary 

 medium traces of mineral acids, of salicylic acid, etc., was 

 tried. In all cases it was found that a percentage of acid 

 sufficient to almost entirely inhibit the development of 

 Bacteria was insufficient to prevent the formation of 

 fungus mycelia or the appearance of Yeast cells and yet 

 prevented the germination of the pollen grains. It is 

 interesting in this connection to notice that cultures of 

 pollen soon became acid and hence in cultures where a 

 vigorous and rapid growth af the pollen tubes takes place 

 the excessive development of Bacteria is to a certain 

 extent checked. Similarly using other poisonous sub- 

 stances (mercuric chloride, sodium arsenate, alcohol, etc.) 

 it was found that any reagent powerful enough to inhibit 

 the development of Yeast, Bacteria and Fungi was also 

 sufficiently powerful to inhibit the germination of the 

 pollen grain and the formation of the pollen tube. 



By adopting certain precautions a fairly pure culture of 

 pollen tubes may be obtained. The sugar solution should 

 be boiled before using, all vessels and instruments used 

 should be previously heated to 150°C and the pollen 

 should be taken not from dehisced anthers but from 

 anthers which are just about to open, whilst the tubes 

 containing the culture should be plugged with sterilized 

 cotton wool. In this way cultures may be obtained in 



