172 Hill. — On the Seed ling- Structure of certain Piper ales. 
variation. The protoxylem may become exarch during the inward pas- 
sage ; sometimes the final disposition is reached by the dying out of the 
accompanying metaxylem. Further, in one case, it was observed that 
the cotyledonary xylem enters the central cylinder as an endarch mass, 
the exarch position of the protoxylem being arrived at by the metaxylem 
bending roun J and taking up a morecentral position. 
The transition takes place very quickly, and an endodermis makes its 
appearance directly it is accomplished. 
Saururus ceriums , Linn. The petioles of the cotyledons form a tube 
round the axis as in H. cordata , and, as the transition phenomena are also 
identical with those of the latter, no detailed description is called for. 
The only point to be remarked is that in one plant the phloem of the 
bundle of one cotyledon, not of the other, exhibited a bifurcation in the 
base of the petiole. 
Houttuynia and Saururus thus resemble Peperomia , and they, together 
with Piper , on the whole, conform to Van Tieghem’s type 3. 
Theoretical. 
The first question of theoretical interest is whether Peperomia is to be 
considered as a primitive or a reduced form. Campbell 1 maintains that in 
Peperomia we have to deal with the most primitive type of Angiosperm 
yet discovered, and that the peculiarities of the embryo-sac are not 
reductions, but consist of an increase in the number of parts. On the 
other hand, Johnson 2 in his work on the embryo-sac of Peperomia ex- 
presses himself as follows : ‘ That these peculiarities are to be considered 
primitive rather than higher specializations seems to me unwarranted by 
the evidence at present available, especially when we consider the fact, 
which I have ascertained, that such closely related genera as Piper , 
Heckeria , and Saururus 3 have essentially typical angiosperm embryo- 
sacs. ... I am inclined to believe that the peculiarities of the embryo-sac of 
Peperomia have been secondarily acquired, and are analogous to those 
found in other angiosperms of peculiar habit, e. g. many aquatic, parasitic, 
and saprophytic forms.’ 
Finally, Johnson 4 has recently expressed the opinion that the develop- 
ment of the megasporangium and the female gametophyte of Angiosperms 
is an unsatisfactory index of genetic relationship, inasmuch as it may vary 
1 Campbell, D. II. Die Entwickelung des Embryosackes von Peperomia pellucida. Ber. 
d. deut. Bot. Gesells. xvii, 1899. 
Campbell, D. H. The Embryo-sac of Peperomia. Ann. Bot., xv, 1901. 
2 Johnson, DuncanS. On the Endosperm and Embryo of Peperomia pellucida. Bot. Gaz.,xxx, 1900. 
3 Johnson, Duncan S. On the Development of Saururus cernuus. Torrey Bot. Club Bull., 1900. 
See also On the Development of certain Piperaceae. Bot. Gaz., xxxiv, 1902. 
4 Johnson, Duncan S. Seed Development in the Piperales and its bearing on the Relationship of 
the Order. Johns Hopkins Univ. Circ. No. 178, 1905. 
