1908] THIESSEN—DIOON EDULE 369 
age has developed about nine or ten leaf primordia, but only about 
one-third have developed into leaves. 
INTERNAL STRUCTURE.—During germination, in connection with 
the development of the primary root, not all of the tissue of the tip of 
the plantlet resumes growth, but only the plerome and a limited 
portion of the periblem or cortex surrounding it becomes meristem- 
atic and pushes through the hard and caplike tissue at the tip of 
the embryo. The cortex which does not resume growth, as well as 
the caplike tissue, frays off (fig. 9, jr). Also, as growth progresses, 
the outer layers of the newly formed root, some distance back of the 
Toot tip, keeps on fraying off; and underneath a phellogen soon 
appears and a layer of cork several cells thick is formed. Along each 
of the four protoxylem strands of the root, continuous from the 
vascular plate, lateral roots have their origin at definite intervals, 
being arranged in four rows. Certain cells among and near the 
Protoxylem elements become meristematic, and form the tip of the 
lateral root, which pushes through the cortex. 
The vascular cylinder increases in dimensions uniformly with the 
growth of the seedling as a whole. New bundles are inserted as new 
leaf primordia appear, and gradually fill in more and more the 
vacant spaces between the original strands, so that immediately above 
the original plate the vascular cylinder is quite compact, while beyond 
this it continues to be represented by separated strands in the potential 
vascular tissue. 
The vascular strands of the cotyledons.—Not much need be added 
'o the statements in reference to the cotyledonary strands. The 
transition from endarch to exarch xylem is very much more gradual 
and the mesarch stage is located relatively much farther up. This 
S due to the fact that most of the growth of the cotyledon in length 
Sccurs at its lower extremity. No secondary wood is developed in 
cotyledons. The phloem also has increased in bulk, but mature sieve 
tubes are never developed. : 
The leaves and scales.—As said above, not all the primordia de- 
Velop into leaves, most of them remaining abortive and forming scales. 
hough about one-third of the primordia develop leaves, it does not 
follow that every third primordium becomes a leaf in regular succes- 
Sion. It sometimes happens that two leaves are developed from 
