Griffin. — Development of New Zealand Conifer Leaves. 47 



while on the lower side there is a tendency to elongation parallel 

 to the surface. The cells in between these two layers are elon- 

 gated in the direction of the margins, which is very desirable, 

 considering the distance there is between the bundles and from 

 these to the margins. Here and there between these elongated 

 cells we find ordinary parenchyma cells, which are often seen 

 in transverse section to form lines stretching across at right 

 angles to the elongated cells. These cross-rows probably serve 

 for quicker communication between the upper and lower sur- 

 faces. None of the elongated cells show any signs of lignifi- 

 cation, which cannot be expected at this stage of development. 



Vascular bundles : There is no sharply marked off endo- 

 dermis roimd each bundle ; the pericycle is one or two cells thick. 

 The protophloem forms a well-marked crescent-shaped zone of 

 crushed elements, while the active phloem elements are arranged 

 in three or four radial rows. The sieve-tubes at this develop- 

 mental stage are long and narrow elements which still have 

 nuclei and horizontal transverse walls. Above the phloem are 

 the xylem tracheids. These are spiral or pitted elements, or 

 elements with both spiral markings and bordered pits, which 

 latter commonly occur on the oblique end walls. On the ventral 

 side of these elements we find the protoxylem with more or 

 less irregular and crushed spiral thickenings. At the sides of 

 the xylem are one or two rather larger elements, the transfusion 

 tracheids ; while occasionally an element is found on the ventral 

 side of the wood, which therefore corresponds to centripetal 

 xylem. Sacs containing a substance with tannin reaction also 

 occur at the sides and on the ventral side of the bundle in the 

 pericycle. I may mention in passing that these sacs have very 

 much the appearance of large tracheids under certain treat- 

 ments, but there can be no doubt of their nature when they 

 are treated with ferric chloride. 



It is rather interesting to note the gradual decrease of tra- 

 cheids in the bundle towards the apex. In a section very near 

 the apex we find the number reduced to six or seven, whereas 

 near the middle and base we find as many as twenty. The 

 number of transfusion tracheids at the sides has increased, 

 for we find groups of twos and threes against the one or two 

 in the middle section. These elements have spiral and pitted 

 markings, which are seen in transverse section on the slightly 

 oblique transverse walls. 



Older Cotyledon. — Transverse section : This presents typically 

 the same appearance as the preceding section. It is charac- 

 terized, however, by a much thicker cuticle and by thicker 

 epidermal walls. The thickened hypoderm also appears along 

 the sides here and there as one or two isolated cells. The pali- 



