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? (821.) 
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 
