The Structure and Development of Internal 

 Phloem in Gelsemium Sempervirens, Ait. 



(WITH PLJ.TE IX.) 



By Caroline B. Thompson, B. S. 



THE following is the result of observations made during 

 the winter of 1897-98, in the Botanical Laboratories of 

 the Biological Department of the University of Penn- 

 sylvania. The material used consisted of specimens of varying 

 age, preserved in alcohol, which had been collected by Pro- 

 fessor Macfarlane, while on a trip to Wilmington, N. C, and 

 of seedlings grown in the greenhouses of the department 

 from seeds collected by him. An abstract of the observations 

 upon the stem was read at the meeting of the " Society for 

 Plant Morphology and Physiology," held at Ithaca, N. Y., 

 in December, 1897. 



General Literature. 

 In the early years of the present century much confusion 

 existed in regard to the terms for the softer elements of a vascu- 

 lar bundle. These were variously called bast fibres, bast cells, 

 latticed cells, sieve fibres, etc. Hartig, in 1837, was the first to 

 correctly describe such elements as sieve tubes, and to regard 

 them as the essential constituents of the phloem. Several years 

 later, Hartig' s observations were confirmed by von Mohl, 

 Nageli and Hanstein. The inves-tigation of plants with internal 

 phloem, or phloem on the inner margin of the wood, was be- 

 gun by Hartig in 1854, and continued by others. The orders 

 Cucurbitacese, Asclepiadaceae and Apocynacese were among 

 the first to be studied. In 1875 de Bary originated the term 

 " bicollateral bundle," a name that has been objected to by 



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