CHAP, m.] PROTECTIVE ARRANGEMENTS. 



95 



the Mesozoic period ; their decline is first indicated in 

 cretaceous times, and since that period up to the present 

 has been increasing. A few representatives yet remain, 

 but, as is well known, they do not stand in the first rank 

 of plants either structurally or numerically, being quietly 

 superseded by the group known as Angiosperms, charac- 



7\ 



T 



L 



Fig. 27. A portion of one of the large olive-brown seaweeds (Fucus 

 vesiculosus), showing the air-containing cavities, L, that act as floats 

 or buoys; T, thallus or vegetative portion; F, fruit-bearing tips. 

 (Natural size.) 



terized by having the seed inclosed from the earliest 

 stage in a special structure, the fruit, and including the 

 great bulk of vegetation existing at the present day. 



Submerged aquatic plants show the least amount of 

 specialization in connection with protection against either 

 enemies or climate, and in such primitive groups as the 

 Algae protective arrangements are almost entirely absent; 



