1912] PFEIFFER—LEITNERIA 197 
interior (fig. 16). Finally the cells were so packed with material 
that it was impossible to distinguish even the nuclei. 
As the endosperm nuclei began division, growth in all parts of 
the ovule became very rapid, and this rapid rate of growth con- 
tinued up to the maturity of the seed. While this was going on 
the reserve material in the nutritive layer began to disappear gradu- 
ally, and as it went the cells of the perisperm immediately above 
it, which had increased considerably in size, were seen to contain 
numbers of starch grains (fig. 17). 
Coincident with the differentiation of the nutritive cells is the 
development of the conducting cells immediately belowit. Fig. 14 
shows the elongation of the cells of this region, and their general 
relation to the nutritive layer when it could first be distinguished 
in the condition of the ovule seen in fig. 13. Somewhat later the 
thickening of the walls of these elongated cells to form tracheary 
tissue was seen (fig. 18). At the time when the nutritive layer is 
most conspicuous on account of its large amount of reserve material, 
a section tangential to the disk of nutritive cells immediately below 
it shows the conducting tissue in the form of a radiating plate of 
tracheary tissue (fig. 19), so that very often in the longitudinal 
section through the ovule there were found transverse and oblique 
sections of the vessels rather than longitudinal as seen in fig. 17. 
At maturity the seed consisted of an embryo with two thin, 
very broad cotyledons. About the embryo was a considerable 
mass of large-celled endosperm tissue whose cells were packed with 
starch. The perisperm was a relatively thin layer of loose tissue. 
These regions, as well as the relative thickness of the seed coats, 
are seen in the diagram (fig. 12). Immediately outside of the 
epidermal layer of the nucellus there is a thick layer of cutin, which 
entirely covers the micropylar end of the seed. So closely abutting 
this layer of cutin that it is impossible to tell whether it was laid 
down by these epidermal cells of the nucellus or by the innermost 
layer of cells of the integument, lies the inner integument. It 
seems probable that the cells of both these closely abutting layers 
may have contributed to the layer of cutin lying between them. 
These cells of the innermost layer are the only cells of the inner 
integuments which are at all conspicuous. In these cells the walls 
