2<594 Journal of Applied Microscopy 



Describe each. What is the condition of the calyx ? Why should the outer 

 flowers develop as ray flowers rather than the inner ones ? Note that the ray 

 flower is zygomorphic. 



LXXXVI. Taraxacjwi taraxacum (L.) Karst. Dandelion. 



Family, Compositae. 



The dandelion blooms from early spring to late autumn, so plants may usually 

 be obtained without difificulty. 



1. Sketch an entire plant, showing root, short stem, rosette of leaves, and 

 slender stems bearing heads of flowers. Note that the dandelion is geophilous. 

 Why does it not grow up out of the ground ? How do you account for the 

 rosette habit? 



2. Make a sketch of a single head. Note that all the flowers are ligulate. 



3. Under dissecting microscope draw a single flower. Describe the pap- 

 pus, corolla, androecium and gyncecium. 



4. Draw some of the ripe fruit. Note adaptation for suspension in the air. 

 Of what special advantage is this parachute arrangement ? Note the action of 

 the involucre while the fruit is ripening. 



5. How many seeds in each dandelion fruit? i. e., how many for each 

 flower ? How many seeds are produced on an average-sized head ? About how 

 many heads of flowers are matured from a fair-sized dandelion plant in one 

 season ? 



6. Suppose that you had one mature dandelion plant and that it produced 

 seed normally for ten years and that each seed developed into a mature plant 

 and began to reproduce at the normal rate at three years of age, how many off- 

 spring would there be at the end of ten years ? 



7. The total land surface of the earth is about fifty-three millions of square 

 miles. Supposing that it were possible to distribute the seed uniformly over the 

 land surface and that all seeds had a suitable environment for sprouting and 

 growing into mature plants, how many dandelion plants would there be for each 

 square mile of land surface at the end of ten years ? 



8. Note. — The above problems will indicate to some extent the great possi- 

 bilities of reproduction present in many plants. It will be remembered that 

 each seed contains a little, dormant embryo ; therefore, every seed that perishes 

 means the destruction of a young plant. It is evident that a very large percent, 

 of young plants must perish each year, and that those which survive for any 

 length of time must usually undergo a severe struggle for existence. In this 

 struggle for life and place the fittest usually survive ; i. e., those which are able 

 to grow more vigorously and thus overshadow their weaker neighbors and those 

 which are best able to adapt themselves to their environment, 



APPENDIX TO ANGIOSPERMS. 

 LXXXVII. Compar-ison of Carpels. 



1. If not previously studied, draw a carpel of Cycas revohita L. 



2. Draw a carpel of the Kentucky coffee-bean {Gymnocladus dioica (L.) 

 Koch). 



