260 HISTOLOGY OF STEM OF THE WAX PLANT 



extending to Sikkam, as one specimen was found, without any indica- 

 tion of its precise station, among Dr. Hooker's collection from that 

 country." 



The plant was described by Schrank as Schollia carnosa, and by 

 Jacquin fils as S. crassifolia; these two names are probably both 

 subsequent to that given by Brown. Miller, in the " Gardener's Dic- 

 tionary," calls the plant the " Fleshy-leaved Swallow Wort." Loudon, 

 in the "Hortus Britannicus," states that it was introduced into Britain 

 in 1802 ; and in the " Encyclopedia of Plants" that " one or two plants 

 placed when in flower in a vinery of ripe grapes will entice the wasps 

 from eating the ripe fruit." In the Botanischer Jahresbericht, 1881, 

 it is stated that the honey of Hoya kills bees. 



Darwin, in his investigations on climbing plants, speaking of the 

 gradation of twining plants to simple root climbers, mentions that 

 Bignonia Tweedyana and Hoya carnosa revolve and twine, but like- 

 wise emit rootlets which adhere to any fitting surface. The plants 

 I have had showed no aerial roots, with the exception of a large one 

 that had been trained over a wooden support, and developed a number 

 of rootlets w^here the frame and the plant had been for a long time in 

 contact. 



General Description of the Stem 



PI. I, Fig. I. PI. II, Fig. 4 



For convenience in description, the stem of Hoya carnosa may be 

 divided into the following zones of tissues, which are best seen in a 

 section about 4 mm. in diameter. Proceeding from the periphery 

 to the center we have : — 



1. The epidermis with its hairs, stomata, etc., composed of one 

 row of polygonal cells with the thick cuticle on the outside. The 

 lateral walls are much thinner, and the cell is completed by one or two 

 walls which are contiguous with the next row of cork cells. 



2. The cork, composed of one or more rows of rectangular cells. 



3. A broad band of parenchyma containing many intercellular 

 spaces. 



4. A ring of sclerotic cells, called by Davids the sclerotic girdle, 

 in a stem of the above size, generally consisting of two rows of cells, 

 which are lignified, and resemble closely the sclerotic cells of the pear. 



5. A broad band of parenchyma, similar to the third ring, 



