304 Introduction to Botany. 



187. Weigh a piece of dry Spanish moss. Dip it into 

 water for a moment and then shake and filter away the 

 water which clings to its surface, and weigh again. Does 

 it absorb water quickly enough to profit much by the rains 

 which fall upon it ? 



DISCUSSION. 



184. Advantages of Complex Structure. — Under normal 

 conditions of soil and climate, the complex body which we 

 find in the higher plants is better adapted to utilize materi- 

 als and forces than the plants of simpler construction, such 

 as mosses and Algas. This is due to the fact that the dif- 

 ferentiation of the plant body into distinct kinds of tissues 

 has permitted division of labor, so that one part of the 

 plant may rise into the free atmosphere and light, and ob- 

 tain to best advantage what they have to offer, while 

 another part may burrow into the soil, and draw from its 

 reservoirs of water and mineral substances. The above- 

 ground parts of such plants are protected against too great 

 transpiration by waterproof outer layers of cells in the 

 form of epidermal or cork tissues. They are equipped to 

 withstand the stress of storms by strong wood and bast 

 tissues ; and the relatively long distances between the 

 aerial and subterranean supplies of food are connected by 

 suitable systems for transportation (see chapters on Roots, 

 Stems, and Leaves). 



185. Result of Unfit Environment. — We see at once 

 how well adapted these plants are to the position in which 

 we find them ; but if they were submerged in water they 

 would die. The waterproof tissues on their exterior which 

 are so beneficial to them in their natural habitat would pre- 

 vent the relatively small amount of oxygen dissolved in 

 the water from being taken up in sufficient quantities to 



