1909] COULTER—EVOLUTION AMONG GYMNOSPERMS gI 
In the first place, the integument and nucellus, instead of remain- 
ing separate, develop separately only in the region of the nucellar 
beak. So early was this change that it probably represents the con- 
dition of the majority of the Paleozoic ovules, a condition which has 
persisted ever since. The method of development is very evident, 
the integument appearing first as a distinct annular growth about the 
base of the young nucellus, but later its basal meristematic zone 
_ becoming indistinguishable from that of the nucellus. In all proba- 
bility the change was brought about by the earlier appearance of the 
integument, and the result has been more or less variability in the 
amount of freedom from the nucellus. 
The three-layered testa persists remarkably throughout gymno- 
sperms, varying chiefly in the amount of development of the outer 
fleshy layer. The stony layer is always strongly developed, and at 
the maturity of the seed the inner fleshy layer always forms for it a 
papery lining. A strong development of the outer fleshy layer, result- 
_ ing in fleshy seeds, continues throughout the cycadophyte phylum 
__ and the Ginkgoales and is a feature of many of the Taxaceae. Among 
the Pinaceae the outer fleshy layer is present in the young integu- 
ment, but does not develop, so that the stony layer is the conspicuous 
superficial feature of the seed. The development of the outer fleshy 
layer among the Cycadales and Ginkgoales is phylogenetically con- 
tinuous from the Cycadofilicales and Cordaitales; but among the 
Taxaceae there is probably no such continuity, but a reappearance 
of the activity of this layer in certain genera. Among the Gnetales, 
the single integument of the other gymnosperms is replaced by two 
_ integuments, the inner fleshy layer having become differentiated as 
_ a delicate inner integument, which appears earlier than the heavier 
_ outer integument, which gives rise to the outer fleshy and stony 
__ layers. In Gnetum the outer fleshy layer develops the pulpy invest- 
ment characteristic of the primitive seeds; but in Ephedra this layer 
behaves as among the Pinaceae. If any general tendencies can be 
inferred from these facts in reference to the integument and testa 
9 they are seen in the abortion of the outer fleshy layer in the largest 
4 group of living gymnosperms, and in the final differentiation of the 
_ three-layered integument into two integuments. 
The vascular supply of the ovule exhibits a very evident progressive 
