5T4 
PHANEROGAMS. 
carpeae iheir capacity for transport is increased by the vesicular hollow protrusions 
of the extine, as represented in Fig. 351, /F, F, bl. [The pollen-sacs (microspo- 
rangia) of the Coniferae resemble the sporangia of the Vascular Cryptogams in 
the mode of their development. A section through the pollen-sac of one of the 
Cupressineae, for example, shows that it resembles a sporangium of Lycopodium : 
FiC. 350. — Abies pectinaia ; A a male flower, b the delicate bud-scales formino- a perianth, a the stamens ; B a pollen-grain 
(after Schacht), e its extine, forming- the two large vesicular protrusions bl. 
in the centre is a group of sporogenous cells surrounded by a layer of flattened 
tabular cells, the tapetum, and externally is the wall of the sporangium. From 
Goebel's^ researches it appears that the archesporium, in Biota orientalis at any 
rate, is a hypodermal cell, the terminal cell of one of the axial rows of cells of 
Fig. 351.—^ pollen-grain of Thuja orientalis before its escape from the pollen-sac, / fresh, //, /// after lying in 
water, the extine e having been stripped off by the swelling of the intine i ; B pollen-grain of Pinns Pinaster before its 
escape, e the extine with its vesicular protuberances bl. 
which the young pollen-sac consists. Possibly the archesporium consists in this 
case, as in Lycopodium^ of a transverse row of such hypodermal cells. The cells 
of the tapetum are derived here, as in Selaginella, partly from the archesporium 
and partly from the tissue of the wall of the pollen-sac. In Pinus the pollen-sac 
^ [Goebel, Vergl. Entwick. d. Sporangien, Bot. Zeitg., 1881.] 
