34 BIOLOGICAL SOCIETY OF WASHINGTON. 



member of the Cretaceous. So late did this now overshadow- 

 ing type of plant life appear upon the globe. The rapidity 

 with which it advanced, conquering and supplanting all rivals, 

 may be better understood when we remember that it forms 

 eighty-five per cent, of the flora of the Dakota group, which 

 corresponds to the Middle Cretaceous. 



A new and vigorous type of vegetation had been developed, 

 the genealogical vine had put forth a fresh branch, the plant 

 world had acquired a new lease of life, and it seems to us, 

 looking back over its history, to have actually taken a leap for- 

 ward at about this epoch, and ever after to have marched on 

 with enormous strides. 



Development of Floral Envelopes. — The resources of improve- 

 ment in organization were, however, not yet exhausted. The 

 germ was, indeed, now protected, and might acquire within its 

 safe chamber all the subtle shades of perfection possible, but 

 the delicate floral organs by which the fecundation of this 

 germ was accomplished were still exposed, as indeed, it would 

 seem, to a greater or less extent, they must always be. Yet 

 means of their better protection were possible and were grad- 

 ually adopted. 



Apetaly. — The very earliest flowers were probably destitute 

 of any protecting envelopes (achlamydeous), and some such 

 still exist, but most of the lowest types of dicotyledonous 

 plants are provided with one floral envelope, sometimes reduced 

 to a few mere scales, sometimes with several distinct sepals in 

 a whorl around the essential organs, sometimes with these 

 united at the base, and occasionally with a bell-shaped, funnel- 

 shaped, or even tubular calyx. Such plants are called apeta- 

 lous or monochlamydeous. Paleontology shows that those 

 forms which are now apetalous, especially those in which the 

 flowers are borne in catkins, or are nearly altogether naked. 



