EXTERXAL COXDITIOXS OE PL A XT IJEE. l8l 



openings into the stomata have been transformed, tlirough 

 tliickening of the cuticle, into narrower, deeper channels. 

 These differences are common to many other plants which 

 inhabit indifferently fresh and salt water locations. 



The plants which grow many miles from the sea-shore are 

 also more or less influenced by the salt in the spray which 

 is mechanically lifted by the winds and carried long distances 

 inland. Lighting on the leaves, it has a tendency to draw out 

 the moisture from within and in this way very materially 

 increases the normal transpiration. To guard against this 

 many plants near the sea-shore thicken up both the cuticular 

 and epidermal layers. Where the wind blows somewhat 

 constantly from the sea over the land, these effects may be 

 seen in plants extending from the shore sometimes as far 

 as twenty miles. 



Many strand plants exhibit the same peculiarities as those 

 of the Rhododendrons of the mountains, i. e., they erect their 

 leaves parallel with the rays of the mid-day sun to avoid loss of 

 moisture. This is especially marked in the Mangroves of our 

 Southern coast, which, for a greater part of the day, stand 

 directly in the water. The plants on our New Jersey shore 

 illustrate many of these facts and are quite as interesting for 

 study as those of South Florida. A half-dozen plants of one 

 of our pigweeds {Atriplex littoralis) taken from a salt marsh, 

 potted, and carried to a greenhouse in the city, exhibited the 

 following interesting characteristics: On the salt marshes from 

 which they were taken, all the leaves were rigidly erect, making 

 no shadow with the mid-day sun. But after being watered with 

 fresh water for five or six days in the greenhouse, all of the 

 leaves dropped down to a normal position, presenting their 

 faces to the direct rays of the sun. Upon watering them for 

 several days following with a strong salt solution, the leaves 

 again erected themselves, assuming the precise position in 

 which they had grown on the salt marshes. 



It has long been known, through physiological experimen- 

 tation, that almost any salt or alkaline solution decreases 

 transpiration, because it at once lessens the water supply. The 

 converse is true of acid solutions. This law may be taken as 



