202 MORPHOLOGY 
carrying the sperms to the archegonia, but is simply an absorptive 
organ. 
Embryo. The development of the embryo differs in detail among the 
cycads, but the general features are fairly constant (figs. 457, 458). The 
first stage is that of free nuclear division, resulting in a distribution of 
nuclei through the cytoplasm of the huge egg (fig. 457). For example, 
in Zamia there are eight successive divisions, re- 
sulting in 256 free nuclei. The next stage is that 
of wall formation, which varies in extent, sometimes 
resulting in a tissue which nearly fills the egg, but 
sometimes (as in Zamia) being restricted to the 
lower region of the egg (fig. 458). This tissue, 
which in Zamia occupies the lower end of the egg, 
is the proembryo. The cells behind the tip cells of 
the proembryo begin to elongate remarkably (fig. 
459), forcing the tip cells out of the archegonium 
into the nutritive tissue of the gametophyte (endo- 
sperm), and continue to elongate until they form an 
exceedingly long, tortuous, and often spirally coiled 
massive filament (suspensor), sometimes 5 cm. or 
more long (fig. 460). The tip cells at the end ot 
this long suspensor form the embryo, which develops 
two cotyledons, a constant feature of cycads. in 
the germination of the seed these cotyledons remain 
FIG. 460. Embryo ..,. A t 
of Cycas circinalis, tlim the testa ' 
showing (above) the Changes ^ terminology. In passing from pteridophytes 
remains of proem- . , , .. . ' i . , . ., , . 
, to spermatophytes, it is sometimes confusing to the beginner 
bryonic tissue, the 
lone and coiled sus- * older terminology of the seed plants to the more 
pensor and the termi- recen t terminology of the lower groups. It is important that 
nal embryo. After this change in terms should not give rise to the idea that 
TREUB. there is any change in the character of the structures. The 
following list should prevent any possibility of confusion in 
this transition from one set of terms to another. The real name of the structure, 
as used in the lower groups, is followed in each case by the older name applied 
in seed plants before any such relationship was known : microsporophvll (stamen), 
megasporophyll (carpel), microsporangium (pollen sac), megasporangium (ovule), 
microspore (pollen grain), megaspore (embryo sac), female gametophyte (endo- 
sperm). 
Conclusions. The fernlike characters of the cycads appear in the 
vascular anatomy, mesarch and even concentric bundles still being pres- 
