Plants 503 



however, may lack either stamens or pistils, when they are uni- 

 sexual or imperfect. If they bear only male structures, they are 

 staminate; and if only female structures, they are carpellate or 

 pistillate. Plants which bear both staminate and pistillate 

 flowers are monoecious. In some of the flowering plants the sexes 

 are in separate individuals as they are in animals. In these di- 

 oecious plants, some individuals will be male, bearing only stami- 

 nate flowers, whereas other individuals will have only pistillate 

 flowers and will be female. Intermediate conditions exist in 

 which some of the flowers on a given plant will be perfect and 

 others staminate or pistillate only. Such plants are polygamous. 

 Like animals, plants in which both sexes are present may be 

 considered hermaphroditic whether the flowers are perfect or 

 whether the plant is monoecious. In this respect monoecious 

 plants resemble hermaphroditic animals such as the earthworm 

 in which sperms and eggs are produced within the same animal 

 but in different organs. 



The relationship between the various stages of the life cycles 

 of animals and plants is interesting to consider and has been well 

 stated by G. H. Shull. If we start with the zygote in animals, 

 we find that it develops by numerous mitoses into the diploid 

 animal body or soma. In the higher plants or Embryophyta, the 

 zygote also develops into a diploid body, the sporophyte. In 

 animals, meiosis takes place from certain cells in the animal 

 body, resulting in spermatids in the male and ootids in the female, 

 whereas the similar products of meiosis in the sporophyte of the 

 higher plants are called, respectively, microspores and mega- 

 spores. In some of the lowest plants, such as the Chlorophyceae 

 or green algae, the zygote fails to develop into a mass of sporo- 

 phyte tissue but remains in a resting condition for a while and 

 then divides directly by meiosis to produce spores. In the em- 

 bryophytes, the microspores and megaspores divide and their 

 products undergo a number of mitotic divisions to produce masses 

 of tissue called, respectively, the microgametophytes and mega- 

 gametophytes ; similar divisions of the spores in the Chloro- 

 phyceae produce multicellular gametophytes which are not dif- 

 ferentiated with respect to sex. The microgametophytes and 

 megagametophytes then produce, respectively, the sperm and 

 the eggs, and the gametophytes of the green algae produce both 

 male and female gametes. In animals, however, the gameto- 



