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 stamens are usually six. The rounded, 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- 

 edly, eventually becoming a small stem 

 with a root at one end and a single ru- 

 dimentary leaf at the other. Here this fig. les.— Verti- 

 embryo sporophyte continues its growth flowl'r'^and^pi^tii)?* 

 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 ma}^ be seen 

 in the Strawberry (Fragaria) in which the flower re- 

 sembles that of the Buttercup and the Water Plantain. 



19 



