1906] CHAMBERLAIN—OVULE OF DIOON 335 
stony layer that one could easily regard the former as an adnate 
cupule equivalent to the free cupule of Lagenostoma. In spite of the 
close morphological continuity between the stone and the outer flesh 
during the early development of the integument of most cycads, the 
two layers separate readily at maturity. The carpels of syncarpous 
ovaries of angiosperms become so closely united that the planes of 
fusion seem completely obliterated and the tissues appear perfectly 
continuous, but at maturity the carpels separate along the original 
planes of union. Hence the close continuity of the tissues should not 
exclude the view that the outer fleshy layer of the cycad ovule repre- 
sents a structure which has become adnate to the stony layer. On 
the other hand, the ready separation at maturity must not be urged 
too strongly as an argument in favor of a union at this plane, because 
at maturity the inner fleshy layer of all the cycads also separates just 
as readily from the stony layer, and the inner fleshy layer of the integu- 
ment never separates at all from the lower portion of thé nucellus. 
While it must be confessed that the cycadean integument itself offers 
no conclusive evidence of a double nature, we agree with Miss Stopes 
that it possibly represents a double structure. In regard to the plane 
of fusion we could not agree with her, but think it more probable that 
_ the union has taken place between the outer flesh and the stone. 
Lhe nucellus.—The nucellus is free from the integument only for a 
short distance, the free portion extending little beyond the top of the 
endosperm. The free surface is cutinized and the epidermal cells 
Contain tannin. When very thick sections are cleared in xylol, the 
free portion is limited by a very conspicuous black line. The sharp 
beak closes and hardens immediately after pollination, imprisoning 
the pollen grains in the pollen chamber. After pollination the upper 
Portion in the surface of the nucellus soon becomes marked by brown 
lines caused by the haustoria of the pollen, which never penetrate 
deeply, but lie just beneath the epidermis. In December a consider- 
able mass of tissue separates the pollen chamber from the top of the 
endosperm, in which the archegonial chamber has not begun to form. 
Subsequent growth of the endosperm, together with extensive dis- 
organization of nucellar tissue and also some enlargement of the pollen 
chamber itself, finally destroys all tissues between the pollen tubes and 
the archegonia. The mode of disorganization which results in the 
