ISTichols, A morphological study of Juniperus communis var. depressa. 223 
which, the exosporium, is fibrillär and somewhat thicker than tbe 
inner, homogeneous endosporium. According to Thomson tbe exo¬ 
sporium is suberized, while the endosporium is composed principally 
of cellulose. When viewed from its outer surface the membrane 
presents a speckled appearance, and this in Taxodium led Coker 
(1903 b) to conclude that the coat was pitted. Thomson, however, 
shows that pits are not present. 
Just as the megaspore membrane is homologous with the 
coat of the microspore, the so-called “spongy tissue” is now 
generally recognized to bear the same relation, on morphological 
as well as physiological grounds, to the tapetum of the micro- 
sporangium. Thomson (1905 a) finds that in Gymnosperms “where 
the normal type of membrane occurs, there is present a more or 
less well defined tapetum”. Noren (1907) describes this tissue in 
J. communis , and its history in var. depressa will be only briefly 
referred to here. As in the microsporangium the tapetum is de- 
rived from the non-functional cells of the archesporium. At the 
time of the tetrad division these cells are large and readily dis- 
tinguishable from the surrounding nucellar tissue (fig. 62). They 
have large nuclei and are densely packed with cytoplasm in which 
are imbedded minute starch granules. As the megaspore develops 
the cells of the tapetum divide actively and continue to invest the 
young embryo sac (fig. 71). The layer is still present when 
the cellular tissue of the prothallium is being organized (fig. 74), 
but after this it rapidly disorganizes. 
The archegonium. — According to Noren (1907) the 
archegonia are derived from the superficial cells in the upper part 
of the prothallium. The nucleus of the archegonium initial soon 
div.ides, cutting off a primary neck cell which by subsequent di- 
visions forms usually a single tier of four neck cells. The arche¬ 
gonia vary in number from four to ten, and, as is characteristic 
of the Cupressecie, they are always grouped close together without 
intervening parenchyma, thus forming a single complex. Düring 
the development of the archegonia to their full size the vegetative 
cells at the upper end of the endosperm grow and divide rapidly, 
and as a result of this local activity the prothallial tissue surround¬ 
ing the archegonium complex rises above the level of the neck 
cells, a depression in the tip of the prothallium being produced at 
the bottom of which lie the archegonia. 
Fig. 78 of the present paper represents the archegonium 
chamber in var. depressa in the process of formation. At this 
stage, which is found about one week before fertilization, the 
central cell of the archegonium contains a relatively small amount 
of cytoplasm restricted to the periphery of the cell, thus enclosing 
a large central vacuole. The nucleus lies directly beneath the 
neck cells,, and, while at first it scarcely differs from those in the 
surrounding prothallial cells, it soon becomes distinguishable by its 
large size. 
Shortly before the division of the central cell nucleus to 
form the ventral canal nucleus and egg nucleus the cytoplasm of 
