274. +| PHYLUM XII. CYCADOPHYTA 
watery fluid to the archegone, finally reaching the egg. 
From the fertilized egg there is later developed a little 
sporophyte which is nourished for a 
ir} @ time by the tissue of the surrounding 
‘ gametophyte. In the meantime the 
integument of the sporangium has 
greatly thickened into a mass of tissue 
soft externally and stony internally. 
Fic. 149.— Zamia 
sporophyte and game- When all growth ceases the megaspor- 
tophytes. : : : : 
angium (ovule) with its contained 
gametophyte and sporophyte falls off, as the “‘seed.”’ — 
491. After the fall of the seed when placed in proper 
conditions as to moisture and temperature, the sporo- 
phyte resumes its growth at the expense of the game- 
tophyte (now called “‘endosperm’’), and soon sends out a 
root, and later a green leaf, after which it becomes an 
independent long-lived plant. 
492. The other living Cycads are essentially similar 
in structure to the foregoing. All of the species are 
tropical or subtropical. Many that 
lived in Mesozoic times have long 
been extinct. 
493. In the Mesozoic period there 
flourished a group of Cycads that may 
be called the ‘Flowering Plant An- 
cestors” (Class BENNETTITINEAE), 4. 150—Bennettites 
and which had “flowers” containing 
a central cluster of stalked megasporangia, surrounded 
by a whorl of pinnate microsporophylls. Below these 
were many sterile bracts reminding one of flower-leaves 
(perianth). The resemblance of this primitive flower 
to the flowers of the simpler Flowering Plants such as 
Magnolia, Asimina, Ranunculus, etc., is so great as to 
suggest a genetic relationship. 
