CHAPTER XIII 
DIVISION SPERMATOPHYTA 
The spermatophytes include all the seed-bearing plants. This 
is the most important division in the vegetable kingdom and 
contains the dominant 
plants of our present 
flora. 
In the spermatophytes, 
as in the pteridophytes, 
there is an alternation 
of generations, the con- 
spicuous generation be- 
ing the sporophyte. The 
reproductive cells that are 
produced by the sporo- 
phyte are meyaspores (Fig. 
463)and microspores. The 
megaspores are formed 
in megasporangia called 
ovules, while the micro- 
spores, or pollen grains, 
are found in microspo- 
rangia known as pollen 
sacs (Figs. 206, 481). 
Considerable confusion 
will be avoided by re- 
membering that the word 
ovule is used to designate 
the particular kind of meg- 
asporangium characteris- 
tic of the spermatophytes. 






quent 
ce 
\\ K 6 
Nis = 
WRT Ha : 
B\wterive pe. 
UT RRR ID YEAR 5 
UT RAR EOL EV OO 
RSS RI OSA TIO] 
Saas aL BS IEE 

Fig. 451. Longitudinal section of mega- 
sporangium of pine 
The megasporangium consists of the nucellus 
surrounded by an integument. The nucellus 
is free from the integument only near the 
apex ; within the nucellus is the megaspore 
mother cell, the contents of which are shaded. 
In the opening (micropyle) there are two 
microspores containing male prothalli. (x 100) 
403 
