476 SCIENCE PROGRESS 



contained in them— the surrounding parenchyma frequently being 

 entirely without osazones. 



Taken in conjunction with all the foregoing considerations 

 such results seem to furnish strong evidence in favour of the 

 theory that sugars are translocated in the sieve-tubes. 



The work is being extended to the lower plants with the 

 object of finding out how far sieve-tubes in general serve to 

 conduct carbohydrates. Some results have been obtained 

 which indicate that the sieve-tubes of Gymnosperms and the 

 " leptoids " of Polytrichum function in this way. 



The sieve-tubes of such Algae as Laminaria are also under 

 investigation, and some attention has been paid to other problems 

 of translocation. 



Among the latter are the forms of sugar translocated, the 

 possibility of a periodicity in such translocation of uncombined 

 sugars, and the upward conduction of sugars in the vessels in 

 spring. 



It is hoped that by the study of translocation in the lower 

 plants more light will be thrown upon the conduction of food 

 in general and that it will be possible to arrive at a clearer 

 understanding of the functions of the various tissues of such 

 lower plants. In this connection Lepidodendron is peculiarly 

 interesting. Prof. Seward has suggested that in the living 

 stem of this fossil plant the physiological division of labour 

 might have been different from that which we find in the nearest 

 living representatives of the genus, as in such stems " there is 

 no indication of any tissue which can be identified anatomically 

 with true phloem." This at once suggests that in such plants 

 the conduction of sugars was probably carried out in a manner 

 unlike that in modern plants which possess true sieve-tubes, 

 and provides a further problem in the physiological anatomy 

 of fossil plants. 



Bibliography 



BiFFEN, R. H., The Function of Latex, Ann. Bot. 1897. 



, The CoaguLition of Latex, Ann. Bot. 1898. 



Blackman, F. F., Experimental Researches on Vegetable Assimilation and 

 Respiration. II. On the Paths of Gaseous Exchange between Aerial Leaves 

 and the Atmosphere, Phil. Trans. Roy. Soc. B. 186, 1895. 



Briosi, G., Ueber allgemeines Vorkommen von Starke in den Siebrohren, Bot. 

 Zeit. 1873. 



