PROBLEM 3. Hov) Complex Flams Reproduce 



prothalli that the asexual as well as the 

 sexual stage can be studied only under 

 the microscope. 



(Optional) Reproduction in mosses. 

 Alosses, too, reproduce by asexual and 

 then by sexual reproduction in regular 

 succession; that is, they also have an al- 

 ternation of generations. A moss plant 

 consists of small, green, closely-bunched 

 leaves, and tiny stemlike and rootlike 

 parts. At certain times of the year you 

 may have seen a tall stalk with a spore 

 case (sporangium) at its top attached to 

 this leafy plant. The spore case is filled 

 with many spores which form by asex- 

 ual reproduction. When ripe the spores 

 may become scattered. On the moist 

 earth each spore can grow into a branch- 

 ing chain of cells (called proto77efna), 

 which is green, somewhat like some of 

 the simple algae. Buds form on this 

 thread, and each bud can grow into a 

 leafy moss plant. In time two kinds of 

 reproductive organs are produced by 

 the leafy plants. One kind produces eggs 

 and the other kind produces sperm cells. 

 The sperm cells, like those of the fern, 

 can move about in a film of moisture. 

 Fertilization occurs, that is, the moss 

 plant has sexual reproduction. From the 

 fertilized egg cell, the stalk bearing the 

 spore case described above develops. It 

 looks like a true part of the leafy moss 

 plant; it is really a separate plant which 

 lives as a sort of parasite, getting part of 

 its food from the leafy moss plant on 

 which it grows. 



Vegetative reproduction. If a farmer 

 or gardener wants a crop of potatoes, 

 he does not plant seeds. Neither does 

 the man who raises sugar cane or straw- 

 berries plant seeds. If you have a be- 



447 



Spore case 



Spore case and 

 spores (enlarged) 



Hood of spore case 



Fig. 397 Pigeon-wheat moss. One of the largest 

 mosses, this may hecoiue eight to ten inches 

 high, but is usually smaller. What step iji the 

 life cycle has been omitted froni this drawing? 



gonia or a coleus plant at home and 

 would like to have more of them, you do 

 not ordinarily plant seeds. AH you need 

 to do is to cut off one of the leafy stems 

 and place the cut end in water or moist 

 sand for a few weeks. You will find that 

 roots grow from the sides of the stem 

 and that soon you have a complete plant 

 — roots, stem, and leaves — which will 

 bear flowers just as the original plant did. 

 You can see that this kind of reproduc- 

 tion is not at all like the sexual reproduc- 

 tion you have just been studying. The 

 process is similar to that in which a star- 

 fish develops a new arm when one is 



