48 LLOYD. 



The margins are finely serrate, as is also a low ridge which runs 

 along the middle line on the upper surface. The surface is 

 markedly glaucous, and stomata are found on the upper surface 

 arranged in ten longitudinal rows and on the lower surface in four 

 rows, one row on each side of the two resin ducts. 



A transverse section shows that the epidermal layer, one cell 

 in thickness, is underlaid by a layer of hypoderm, consisting of 

 strengthening cells, which, as a rule, does not exceed one cell 

 in thickness except at the angle of the lower side where an in- 

 complete second layer is found. The resin ducts are two and 

 are in contact with the lower epidermis. 



The parenchyma is of cells of the infolded kind which is 

 characteristic of the group. 



A fibro-vasal sheath is rather weakly developed enclosing two 

 bundles, which are slightly separated, consist of the usual ele- 

 ments and are surrounded by pitted vessels. The vascular 

 bundles are weaker than in the normal leaves, and are closer 

 together. The stomata are in nine to twelve rows on the upper, 

 and in four rows on the lower surface, and the latter are so dis- 

 posed as to be one on either side of the two resin ducts. 



The normal leaves are about 20 cm. long, and, springing as 

 they do in threes from the fascicles, are in transv^erse section the 

 shape of a sector of 120°. Such long, slender " needles" re- 

 quire and possess much stiffening tissue which occurs as hypo- 

 derm of several cells in thickness. The resin ducts, two in 

 number, are here found deep in the parenchyma, opposite the 

 lateral angles. The endodermic sheath is relatively larger and 

 contains two strongly developed vascular bundles which are 

 more widely separated than in the hypertrophied scales. 

 Without and surrounding the bundles is a mass of tissues com- 

 posed of pitted vessels. The stomata occur in twelve rows on 

 the upper and in thirteen to fifteen rows on the lower surface. 



It will be seen then that the abnormal leaves in question 

 differ in the arrangement of tissues quite markedly from the 

 normal. They approach, in fact, very closely to the early or 

 primordial leaves in the species of Pinus described by Daguillon. 

 These latter, however, are in their plan of structure very simi- 



