204 TRANSLOCATION IN PLANTS 



The evidence, however, is as yet inadequate to prove in 

 which region the major transport of sugar or other materials 

 takes place. The observations of Schumacher (1933) on 

 the transport of fluorescein and those of Van der Wey 

 (1932) on the transport of growth substance are of great 

 interest, both for the data given and for the bearing of 

 these on the problem of the mechanism of transport. Their 

 findings might be interpreted to support this hypothesis. 



37. Schumacher's Observations on the Transport of Flu- 

 orescein. — Schumacher (1933) has reported some extremely 

 interesting experiments on translocation in which he used 

 the vital stain, fluorescein. Most of the experiments were 

 carried out with specimens of Pelargonium which had been 

 forced into vigorous growth by growing them in partial 

 shade at high humidity, and by removal of all flower buds. 

 The fluorescein was introduced by placing on the scraped 

 surface of a leaf vein or stem a drop of 5 per cent gelatin 

 containing a 0.1 per cent solution of the potassium salt. 

 The presence of the dye was detected by fluorescence when 

 longitudinal sections were mounted in paraffin oil and 

 examined in a dark room using light of short wave lengths. 

 He found that fluorescein is strongly absorbed by the 

 protoplasm of sieve tubes as well as that of parenchyma 

 cells. The green fluorescence is observable in the nucleus, 

 protoplasmic threads, outer protoplasm, and starch grains 

 of both leucoplasts and chloroplasts. The walls and 

 vacuoles appeared totally dark and devoid of fluorescein. 

 The protoplasm of dead or injured cells does not stain, and 

 the stain is lost from the cells as they approach death. It 

 spreads with great rapidity through the cytoplasm of sieve 

 tubes and much more slowly in that of parenchyma cells. 

 He made the interesting observation that, as the fluorescein 

 was entering the sieve tubes from the gelatin, the com- 

 panion cells were commonly more intensely fluorescent 

 than other cells. This supports the suggestion of Czapek 

 (1897) that these cells are especially concerned in carrying 

 substances to and from the sieve tubes. After entering 

 the sieve tubes, rapid spread is almost exclusively through 



