192 



The Ohio Naturalist. 



[Vol. IV, No. 8^ 



THE JACKET LAYER IN SASSAFRAS. 



John H. Schaffner. 



In the ovules of some angiosperms a definite nutritive tissue 

 invests the embryo-sac, while in others no such layer exists. 

 This nutritive jacket appears in all cases to be simply a modifica- 

 tion of one or more layers of cells on the inner wall of the ovule. 

 It is purely a physiological tissue and is usualh- described as 

 consisting of cells with deeply-staining contents. It is much less 

 definite in structure than the tapetum in the microsporangia of 

 the stamen, but reminds one of the so-called spongy tissue in the 

 ovule of the pines and related plants. Although usually descril^ed 

 as a dark staining tissue, there are examples where just the 

 opposite is the case. Cook ( i ) describes the tissue in the wall of 

 the ovule of Agrostemma githago as consisting of two zones, the 

 inner zone consisting of thin-walled cells which degenerate while 

 the embryo-sac is enlarging. Although the cell walls of the zone 

 were very delicate, the entire layer was sharply separated from 

 the outer tissue by a very thick limiting wall. 



Fig. I. Ovule of Sassafras, showinsj jacket layer, a, cross section ; b, 



longitudinal section. 



While studying some preparations of Sassafras sassafras, the 

 writer observed a jacket of cells surrounding the mature embryo- 

 sac. This layer shows .some resemblance to the delicate zone in 

 Agrostenuna, l)ut there is no distinct limiting wall on the outside. 

 It is from one to several layers of cells in thickness and the cells are 

 light-colored with Delafield's haematox\-lin and Heidenhain's 

 haematoxylin, while the cells of the outer zone stain ver}^ dark 

 (Fig. I , a, b). The cells have large vacuoles and comparatively little 



