22 Russell— Comparison of the Structure of Hybrid 



Longitudinal Section of the Rim 



A longitudinal section through the rim region of S. Drum- 

 mondii shows that the rim is rolled over once as in S. flava, 

 but with no trace of the peculiar flattening on the under part 

 of the turn. The tip is in 5. Drummondii pointed and elong- 

 ated, with thickened cells through the whole tip. The con- 

 ducting cells do not appear until well around the outer curve 

 of the rim ; while in 5. flava they occur at the outermost edge 

 of the rim. In S. Moorei they appear further around the rim 

 than in S. Drummondii. The tip region of 6". Moorei is not 

 so pointed as in S. Drummondii, nor as blunt as in 5. flava; it 

 is between the two. 



There are in 5. Drummondii two rows of thickened cells 

 subjacent to the conducting epidermis. S. flava has only one 

 row of such cells, while in the hybrid there is a complete row, 

 and a second incomplete row. 



The mesophyl of all three types is compact, excepting for 

 the regions of the areolations in S. Drummondii and S. Moorei. 

 Here the tissue is loose, with many air spaces. In S. Drum- 

 mondii the cells of these areas are devoid of contents, but the 

 tissue of this region is as deep as that of the non-etiolated por- 

 tions. In 5. Moorei, in young leaves, these areas are not en- 

 tirely devoid of chlorophyl, so that they appear light green 

 rather than pure white as in S. Drummondii. 



Below the mesophyl there is in S. Drummondii a reversed 

 palisade of 3-4 layers of cells ; in S. flava there are 3-4 layers ; 

 in 5. Moorei, 3 complete and regular layers. 



The outer epidermis of S. Drummondii is swollen into peculiar 

 pointed papillae. These become especially pronounced over 

 the areolations. S. flava has a smooth epidermis, but in S. 

 Moorei a trace of such swellings as are present in S. Drummondii 

 occur. They are here more rounded than in S. Drummondii. 



Detentive Surface 



On the outer part of the conducting and upper detentive 

 areas of 5. Drummondii there are stomata present. They are 

 very sparsely scattered and rather difficult to find. About 

 them is a group of special cells. In counting a hundred fields 

 for detentive hairs, four such stomata were found. In S. Moorei, 



