The Gametophytes and Embryo of the Cupressineae 
with special reference to Libocedrus decurrens. 
BY 
ANSTRUTHER A. LAWSON, Ph.D. 
Assistant Professor of Botany in Stanford University , California , U.S.A. 
With Plates XXIV-XXVI. 
Introduction. 
T HE series of studies on the Gymnosperms which the writer has 
published during the last three years, and of which the present 
memoir is the fourth, was undertaken with the idea that a detailed know- 
ledge of the vestigial structures associated with the gametophyte generation 
might throw some light on the phylogenetic relationships of the various 
sub-groups of the Coniferales, and that the data, accumulated from the facts 
concerning such structures, might eventually be of some service in contri- 
buting to our knowledge as to the origin of the Gymnosperms in general. 
Although the Coniferales are second only to the Angiosperms as a domi- 
nating race of seed-plants, they are, nevertheless, a very ancient group, 
extending, as the fossil evidence would seem to indicate, as far back as the 
carboniferous period. In attempting to construct a phylogeny of a group 
of plants of such great antiquity from a study of recent forms, one must 
naturally rely almost entirely upon a study of those structures, the nature 
of which will throw light upon ancestral affinities. For instance, the pro- 
thallial cells in the microspore, the structures in the pollen-tube, the 
organization and form of the sperm cells, the megaspores, the tapetum, 
the megaspore membrane, the formation of the female prothallium, the 
structure of the archegonia, the ventral canal cell, the process of fertilization, 
and the development of the embryo, all show phases of phylogenetic interest. 
With the exception of the early history of the male gametophyte, all of 
these more or less vestigial structures are buried within the tissues of the 
sporophyte, and therefore are less liable to be modified and specialized 
by external factors, and more likely to preserve characters which are 
obviously primitive than those of the sporophyte. That the sporophyte 
contributes evidence of great value is clearly indicated by Professor Jeffrey’s 
Annals of Botany, Vol. XXI. No. LXXXII. April, 1907.] 
