200 TRANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



the tube into separate segments but may also segment 

 its protoplasmic contents. They may be formed at the 

 base of the tube where the protoplasm has all flowed away 

 towards the apical part of the tube, as well as in regions 

 still filled with protoplasm. 



The formation of these septa seems to be due to a 

 pathological change in certain regions of the wall of the 

 pollen tube. They are shewn best after staining with 

 picric-aniline. If left staining in this reagent for a 

 limited period, the walls and septa are stained blue whilst 

 the protoplasmic contents owing to the picric acid 

 penetrating first are stained yellow, though if left in the 

 stain for a longer time they become yellowish blue. By 

 this method of staining the ingrowths are rendered 

 very conspicuous. The septa are seen on testing micro- 

 scopically to be composed of cellulose. Both the walls 

 of the pollen tubes and the septa formed from them are 

 too delicate to allow the sulphuric acid and iodine test 

 to be employed, the acid either shrivelling up the tubes 

 or totally destroying them. On treating with chloro-zinc 

 iodine solution the walls of the tubes swell up and turn 

 blue, the cavity of the tube being almost obliterated and 

 the septa disappearing. If, however, a septum is watched 

 whilst this reaction is taking place the tube is seen to be 

 at that point solid and blue throughout. The refractive 

 indices of the walls and septa are after treatment with 

 chloro-zinc iodine solution similar though formerly they 

 were not so. The septa being portions of the cell which 

 have already swollen do not swell any further whereas the 

 cell wall under the action of the reagent does swell and 

 its refractive index is now the same as that of the septum. 

 Cupr. -ammonia dissolves both walls and septa. 



On examining a series of living pollen tubes the origin 

 of these septa can readily be made out. They arise in the 



