98 Trans. Acad. Sci. of St. Louis. 



of the light line varies in different plants. It may occur in 

 the testa, the wall of the ovarj, or the wall of a sporangium. 

 In all cases, so far as I am aware, it is connected with a 

 reproductive body, and obviously has some function. It may 

 be of interest to briefly review the theories concerning it. 



Mettenius (407) states that perhaps it originates from the 

 pore-canals all appearing at the same height in these cells, 

 but he was unable to make these out in cross sections. Schlei- 

 den and Vogel (234. 235, 76), in describing the mature testa 

 of Lupinus perennis, L. rivularis, and Acacia Farnesiana^ 

 thought the walls of the upper and lower parts of the cells 

 were unequally thickened, the cavity entirely disappearing in 

 the upper part of the cell. Targioni-Tozzetti (257.-99, 2 : 

 561) suggested that the light line in Vicia pohjantha was 

 due to numerous thickened, refractive points found above the 

 middle; below this a wide cavity with a thin wall. Hanstein 

 (363.-99, 2:561) gives an explanation of the light line 

 in two places. At first he considered that the Malpighian 

 layer consisted of a double row of cells. Later he attributed 

 the phenomenon to a perforated disc at this point, which 

 transmitted the light. 



The earlier accounts of the light line were based on obser- 

 vation. Russow, however, studied the light line under polar- 

 ized light and tested it with microchemical reagents. He 

 concluded that it had a modified molecular structure, con- 

 taining less water than the remainder of the cell-wall. lu 

 Marsilia the light line is anisotropic* Lohde (396) agrees 

 with Russow in regard to the anisotropic nature of the light 

 line. In Convolvulus and Qaamoclit the Malpighian cell, 

 except the light line, colors blue with sulphuric acid and 

 iodine, the parts being less soluble in the region of the light 

 line than elsewhere. In Hibiscus Trionum the light line is 

 cuticularized. 



Sempolowski (247), who investigated the light line in 

 Lupinus and other Leguminosae, states that there is not only 

 a difference in the molecular structure but also a chemical 



* On this general subject see Zimmermann, Beitrage zur Erkliirung d. 

 Anisotropie d. organisirten Substanzen, — in Habilitationschirift, Ueber 

 Zweck u. Mecbanik d. liygroskopischen Gebilde der Pflanzan. Berlin. 



