EXERCISE 96 

 VEGETATIVE STRUCTURE OF A MOSS PLANT 



Materials. Growing moss plants collected by the class on field 

 trips ; preserved materials to supplement the collections if necessary. 



Directions for work. Study the plants with the object of 

 finding out how well fitted they are to perform their nutritive 

 work in competition with other plants and in the struggle against 

 unfavorable natural conditions. Compare constantly with what 

 you know of simpler plants (algse) and more complex plants 

 (flowering plants). 



1. How does the moss plant secure food? Does it have 

 chlorophyll ? stem ? leaves ? In what way, if any, is it better 

 equipped than the common algse to expose a large surface to 

 the light without being readily shaded ? In a competition for 

 light between an alga like Spirogyra and a moss growing in the 

 water, as peat moss, which would probably survive ? Which, 

 in the case of a land alga, like Pleurococcus or Vaucheria, and 

 a common moss ? 



Would a moss or a flowering plant have the better oppor- 

 tunity to secure light and carry on photosynthesis? Can you 

 find in the moss plant strengthening tissue such as you found 

 in flowering plants, which would support large leaves and tall 

 stems? What is your opinion of the place of the mosses in 

 the competition for light among plants ? 



2. Consider the problems of securing and retaining water 

 in relation to the moss plant, keeping in mind particularly the 

 mosses that live upon land. 



What equipment does the moss plant have for securing water 

 from the soil? Might it be able to secure water from even a 

 very small distance beneath the surface ? How does its equip- 

 ment for absorption from the soil compare with that of the 

 algse ? with that of the flowering plants ? 



How well is the moss adapted to retain water ? Does it have 

 an epidermis, layers of hairs, cuticle, or other protective devices 

 such as you found on leaves and other parts of flowering plants? 

 Would you expect to find a high or a low rate of transpiration 



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