THE DEVELOPMENT OF ORGANISMS 773 



there may be a masked alternation of generations in the life-history 

 of certain animal types like starfishes, butterflies, and even 

 armadillos ? 



LIFE-HISTORIES OF PLANTS 



In higher plants we are familiar with the ascending and descending 

 curve of life, so emphatic in annuals — sprouting, developing, leafing, 

 growing, flowering, fruiting, seeding, withering, and dying. And 

 even when the plant lives on for many years there are on the main 



Diagrammatic Representation of Alternation of Generations. AS, asexual, and 

 S, sexual. II shows a well-defined alternation of separate individuals, 

 asexual and sexual. In I the sexual (S) is becoming increasingly sub- 

 ordinated to the asexual (AS), as in Flowering Plants. In III the asexual 

 (AS) is more and more subordinated to the sexual (S), as in Mosses. 



curve or trajectory the minor ups and downs of leafing and flowering, 

 fruiting and seeding, determined by the seasons. 



Just as among animals there is sometimes a very unusual form 

 of life-curve. This may be illustrated by the Century Plant {Agave 

 americana) which is vegetative for a long stretch of years, sometimes 

 for a whole human generation, and then suddenly bursts into a 

 gorgeous inflorescence and dies! In the basal rosette of large leaves 

 there is an accumulation of nutritive reserves and water; on the 

 strength of this a gigantic flower-stalk rises many feet into the air, 

 and as it grows and blossoms the basal leaves fall back limp and 

 moribund. After the ripening of the fruit, the Century Plant, 



