186 



BOTANY: PRINCIPLES AND PROBLEMS 



Chromosome Reduction. — Certain noteworthy differences occur 

 between the cell division which preceeds the formation of the 

 gametes and those which we have studied in the ordinary 



Fig. 98. — The structure of a flower of a monocotyledonous seed-plant {Tril- 

 lium). A, face view of the flower showing calyx of three sepals; corolla of three 

 petals; 5 stamens, and the pistil. B, side view of the flower with one petal and 

 one stamen removed. C, a transverse diagram of the flower, the sepals and ovary 

 walls black, the petals, stamens and ovules outlined. D, a longitudinal diagram 

 of the flower. 1, sepal. 2, petal. 3, stamen. 4, pistil. 



Fig. 99. — Pollen grains of various types. A,Circaea. B,Cobaea. C, Morinda. 

 D, Cucurbita. E, Pinus. F, Dianthus. G, Gentiana. H, Corydalis. I, 

 Nymphaea. J, Taraxacum. K, Buphlhalrmmi. L, Hibiscus. ' 



vegetative tissues of the plant ; and a knowledge of these differ- 

 ences is essential to a thorough understanding of the laws of 



