WATER PLANTAIN 289 
its stem and leaves to the light above ground, and be- 
comes an independent plant (sporophyte). 
525. The flower structure of the Water Plantain 
(Alisma) is essentially the same as that of the Buttercup. 
In it the flower axis is less enlarged, the carpels are 
fewer, in only a single whorl (i.e. not spirally arranged), 
and the stamensare usually six. Therounded, white petals 
are in a whorl of three, and the pointed, green sepals are 
also in a whorl of three. In the single ovule the develop- 
ment of the megaspore and later of the egg is similar 
to that in the Buttercup, as is also the growth of the 
. pollen tube, and the process of fertilization. The 
endosperm develops as a belated gameto- 
phyte, and the zygote divides repeat- Soy 
edly, eventually becoming a small stem 
with a root at one end and a single ru- (7 
dimentary leaf at the other. Herethis fre. 163—verti- 
embryo sporophyte continues its growth oman 
until it has absorbed all of the endo- 
sperm: as a consequence it is much larger than in the 
Buttercup, and the seed at maturity contains no 
endosperm. 
526. The structure and behavior of the fruits (ripened 
carpels with their contained seeds) are in no wise unlike 
those in the Buttercup. So too the germination of the 
seed inside of the ripened carpels is similar to what has 
been described above. However, as there is no more 
endosperm remaining in the seed, the embryo escapes 
from it shortly after the root has appeared and pushes 
up its stem and leaves to the light above ground, as an 
independent plant (sporophyte). 
527. A third example of a typical flower may be seen 
in the Strawberry (Fragaria) in which the flower re- 
sembles that of the Buttercup and the Water Plantain. 
19 
