18 BOTANY 



fundamental when one goes back to the origin of things, 

 for the simplest kinds of plants have only two kinds 

 of cells, the vegetative and the sporangiate. 



These reduced leaves of the flower and their spore 

 sacs are called stamens ; the pollen grains, or spores 

 which they produce, contain the male nuclei. The re- 

 duced stalk-like " leaves " of the stamens have a 

 great tendency in many flowers to enlarge and become 

 petal-like. The large flowers of the Rhododendron 

 commonly show many intermediate stages between 

 ordinary petal leaves, through half reduced petals 

 with one or more anthers, to the normal stamens. The 

 "doubling'' of Buttercups, Cherries, and such flowers 

 is due to the greater part or all of the stamens becoming 

 petaloid. When the doubling is complete the flower 

 cannot produce any pollen of its own, and must either 

 be pollinated from the single flowers or remain sterile. 



We have spoken of the production of the male nuclei 

 in the pollen, and this, of course, presupposes the ex- 

 istence of a female cell with which it can fuse. These 

 female cells are produced in " ovules," which are con- 

 tained in one or more cases or carpels lying in the centre 

 of the flower. These structures are exceedingly complex, 

 and the details of their morphology require much study, 

 and are still the subject of investigation and discus- 

 sion. There is, however, no doubt that the closed cases 

 or carpels which contain the ovules represent a leaf 

 in which the edges have rolled over and joined up to 

 form a little bag-like structure. This may be entirely 

 closed, or may tend later to split open again, as it does 

 in the Larkspur, for example, when the seeds are ripe. 

 The unfertilised seeds or ovules containing the egg- 

 cell develop on the inner edges of the carpel leaves, 

 and are thus protected by the closed bag they form. 



