PAM.MEL— ON THE SEED-COATS OF EUPHORBIA. 55^ 



In Poinscttia. H. dentata and R. hctcrophylla were studied. 

 The seeds are shown on plate xii. , figures 13 & 14. E. dentata 

 is less tuherculated. In E. heterophylla the ripe seeds may be 

 of pale color or blackish. The pale color is due to the white mu- 

 cilaginous layer covering them, which, after exposure to water, 

 has exfoliated, showing the dark palisade-like layer under- 

 neath, thus giving to the seeds a darker color. A cross-sec- 

 tion^of E. heterophylla is shown on plate xiii., figure 11. The 

 cell-walls are nearly colorless, and the cell-cavity is very much 

 reduced. The pores of the palisade-like cells are well developed. 

 The granular layer contains the usual granules, which show the 

 starch reaction. The layer next to the endosperm is very much 

 compressed, and the cells are elongated and thin-walled. 



The general character of the seeds of E. dentata is much like 

 that of the last species. (See plate xii., figure 13.) A cross- 

 section of the seed is shown on plate xiii. ; at figure A, a gen- 

 eral outline of the ridges and the depressions. These points are 

 caused by the cells, which project like little papilla ; the num- 

 ber of cells is somewhat variable. The cell-walls are colorless, 

 and the cell-cavity is filled with a brown substance as in the last 

 species. The palisade-like cells are well developed ; the pores 

 are conspicuous and come out clearly. Next to the endosperm 

 is a layer of cells provided with thickened ridges, such as occur 

 in E. marginata and E. hexagona. 



The following species of Tithy7nalus were studied : E. obtu- 

 sata^ E. Cyparissias^ E. commutata^ and E. Lathyris. 



The seeds of E. obtusata are blackish and smooth. A cross- 

 section shows that the outer cells appear somewhat like papillae in 

 places. The cell-walls are colorless (PI. xiii., figure 5 A) and are 

 provided with pores (5Ba). Between the palisade cells and this 

 layer several rows of thin-walled elongated cells occur : these, on 

 account of compression, are indistinct. The palisade cells are of 

 the usual kind : they are followed by thin-walled elongated cells, 

 also very much compressed. 



The smooth and dark colored seeds of E. Cyparissias are 

 shown on plate xii., fig. i8c; cross-section of the seed, on plate 

 xiii., fig. 16. The seed shows the usual palisade-like cells, and 

 the overlying and u derlying parenchyma cells. 



