354 PRACTICAL COURSE IN BOTANY 



nate the two groups are : (1) the presence in Pteridophytes 

 of a highly organized vascular system accompanied by a 

 well-marked differentiation of the plant body into root and 

 stem ; (2) increased importance and complexity of the sporo- 

 phyte with proportionate diminution of the gametophyte. 



While vessels for conducting water occur in some of the 

 bryophytes (403), a well-defined vascular system and true 

 roots are met with first in the Pteridophytes. The change 

 in the relative importance of sporophyte and gametophyte 

 is so marked that in Selaginella, the genus which approaches 

 nearest in structure to the seed-bearing plants, the suppres- 

 sion of the gametophyte has proceeded so far that it never 

 leads an independent existence at all and is difficult even to 

 recognize as a distinct individual. 



Practical Questions 



1. Have ferns any economic use that is, are they good for food, 

 medicines, etc. ? 



2. What is their chief value ? 



3. Under what ecological conditions do they grow ? 



4. Are they often attacked by insects, or by blights and disease of 

 any kind ? 



5. Of what advantage is it to ferns to have their stems underground, 

 in the form of rootstocks? (321.) 



6. What causes the young frond of ferns to unroll ? (54, 98.) 



7. Name the ferns indigenous to your neighborhood. 



8. Which of these are most ornamental, and to what peculiarities of 

 structure do they owe that quality ? 



9. Are cultivated ferns usually raised from the spores or in some 

 other way? Why? 



10. After the great eruption of Krakatao in 1883, by which the vege- 

 tation of the island was completely destroyed, ferns were the first plants 

 to reappear. Explain why. (19 ; Exp. 17.) 



VIII. THE RELATION BETWEEN CRYPTOGAMS AND 

 SEED PLANTS 



413. No break in the chain of life. -- The great gap that 

 was once supposed to exist between the cryptogams and 

 phanerogams has been bridged over by the discovery of 



