THE SPERMATOPIIYTA 367 



791. Can you suggest why seed plants have so very many more 

 species than either bryophytes or pteridophytes? 



792. From a consideration of the present distribution over the earth 

 of ferns and of primitive seed plants, what suggestion can you make as 

 to the climatic conditions under which the earliest seed plants were 

 evolved ? 



793. Why do you think it is that seed j)lants are not very common in 

 the ocean? 



794. The name "Flowering Plants" is sometimes applied to the seed 

 plants. Why is it not a very satisfactory name? 



795. The archegonium is much reduced in the gametophyte of the 

 seed plants. Explain. 



796. With what in the ferns is the embryo-sac of seed plants compara- 

 ble? the pollen grain? the ovule? the nucellus? 



797. To what in seed plants do the following structures in liverworts 

 correspond: The spores; the sporangium wall and seta; the thallus; the 

 sperms? 



798. Different terms are used for the various structures in the plant's 

 life history among seed plants than are used among bryophytes and 

 pteridophytes (embryo-sac for female gametophyte, anther for sporan- 

 gium, and so on). What reason can you suggest for this? 



799. What great groups of animals are there which obtain the bulk 

 of their food directly or indirectly from other plant groups than the seed 

 plants? 



800. What similarities can you suggest in the evolutionary history of 

 bryophA^tes, pteridophytes, and spermatophytes, in the plant kingdom, 

 to that of amphibians, reptiles, and mammals in the animal kingdom? 



801. What various resemblances do the cycads show to the ferns? 



802. In what way is the relation of the conifers to the rest of the 

 gymnosperms similar to that of the ferns to the rest of the pteridophytes? 



803. What relation can you suggest between the characteristic wood 

 structure of the conifers and the tough and scale-like character of tlieir 

 leaves? 



804. In such a tree as the pine, are the staminate or the ovulate 

 cones more numerous? Explain. 



805. In regions where there are large coniferous forests, "showers of 

 sulphur" sometimes occur in the spring. What explanation can you 

 suggest for these? 



