FACTORS AFFECTING SEASONAL ACTIVITIES. 17 



tensity of external conditions is changed is a basal factor in all 

 accommodation processes. As a plant accommodates itself to 

 live at unwonted temperatures, or in unaccustomed soils, but 

 little doubt exists that it undergoes changes in intricate struc- 

 ture, which, however, are not always to be demonstrated. So 

 long as the species remains under the new and strange conditions 

 the acquired structure will be retained from generation to gen- 

 eration, whether propagated by cuttings or seeds. If the species 

 is returned to its original habitat or to the normal conditions in 

 which it originally grew, the acquired structures may persist for 

 a time, but in accordance with the power of accommodation 

 which originally brought them into existence, they will disap- 

 pear when the inducing factors are removed. 



The classical cultures of Bonnier made in the Alps and 

 Pyrenees, twenty years ago, furnish us with the bulk of the sys- 

 tematic information available as to the influence of elevation on 

 plants. From these it was seen that plants taken from lower to 

 higher altitudes, up to about 7,000 feet, and not exceeding the 

 optimum of the species, developed shorter internodes, the subter- 

 ranean parts of the plant were relatively much larger, the leaves 

 were smaller, more deeply colored, and the flowers were also 

 more vividly tinted. 



No better illustration of the changes in structure shown by 

 plants, when accommodating themselves to habitats presenting 

 strange external conditions, can be found than those found in the 

 American water-cress (Roripa Americana), with which some ex- 

 tensive experimentation has been carried on. Originally taken 

 from the muddy bottom of Lake Champlain, where it grows in 

 water at a depth of I to 3 feet, it had been gradually accommo- 

 dated to the propagating bed, the cold frame, and the hothouse in 

 the New York Botanical Garden, from whence it has been suc- 

 cessfully transferred to the Laboratory at Cinchona, Jamaica, and 

 to the montane plantation of the Desert Laboratory in the Santa 

 Catalina Mountains in Arizona. During this dissemination it 

 has substituted radish-like structures for the bunch of fibrous 

 roots characteristic of it, and developed new forms of leaves and 

 stems, while throughout it shows tissues and arrangements of 

 tissues wholly unfamiliar to it ; all of which has been brought 



