THE NURSERY-BOOK. 



is a difference in time of maturing of the two sexes. In any 

 flower the two parts are rarely ready at the same time. Flow- 

 ers in which the stamens mature first are said to be proteran- 

 drous, and those in which the pistils mature first are proterogyn- 

 ous. In crossing such species, flowers of different ages can 

 usually be found so that the parts can be brought together with- 



Fig. 93. Closed stigma of 

 tecoma. 



Fig. 94. Open stigma of 

 tecoma. 



out difficulty. But when one series of organs in all the flowers 

 of any species perish before the other series is mature, the pol- 

 len must be kept until the pistils are ready, or one sex must be 

 forced or retarded artificially to accommodate the other. If the 

 pollen matures first, it is only necessary to keep it a few days 

 until the pistil is ready ; but if the pistil matures first, and the 

 plants cannot be handled artificially, the pollen must be kept 



