KKRN PLANTS 26 I 



tion of a new strain at each alternation, with the advan- 

 tages of cross-fertilization (Sec. 313). 



370. Microspores and Macrospores. — The method of re- 

 production in other pteridophytes is similar in all essentials 

 to that of the ferns, except that in some of the orders it 

 is even more complicated. The sporophyte, instead of 

 producing spores which are all alike, bears two kinds of 

 fruiting organs called sporophylls (spore-bearing leaves), 

 one of which produces sporangia containing large bodies 

 called megaspores, or macrospores, the other smaller ones 

 called microspores. These large and small spores give rise 

 to different kinds of gametophytes, one bearing arche- 

 gonia, the other antheridia, and it is only by the union of 

 a pair of gametes from each kind that an oospore capable 

 of producing another sporophyte can originate. This 

 complicated arrangement may be expressed to the eye by 

 a diagram something like the following, in which .S stands 

 for sporophyte, G for gametophyte, mgs. for megaspore, 

 mcs. for microspore, mgsph. for megasporophyll, mcsph. for 

 microsporophyll, gam. for gamete, and 00. for oospore. 



(, / mgsph. — >- mgs. — ^ archegonial G. — >"gam.^ ^ .. ^ ^ 



\ mcsph. — >-mcs. — >- antheridial G. — >- gam. / 



PRACTICAL QUESTIONS 



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

 medicines, etc. ? 



2. What is their oliief vahie? 



3. Under what ecological conditions do they grow? 



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

 any Icind? 



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

 in the form of rootstocks? (195.) 



6. What causes the young frond of ferns to unroll? (162, 204.) 



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 ? 



