1 66 BIOLOGICAL LECTURES. 



2. The Light Supply Here again we may have too much 



or too little, either condition leaving its strong impress 

 on the plant. 



3. Altitude i^a third factor in the growth of plants, which 



strongly influences the light, the moisture and the tempera- 

 ture, as we shall see in a later discussion. 



4. Temperature. Temperature and light, together, govern 



largely the transpiration of water from the plant. 

 The character and position of the leaves are often wholly 

 adapted to both the conservation and the loss of water by 

 transpiration. 



5. The Food Supply produces the most fundamental changes 



in the life of the .plant, strongly influencing not only the 

 production and character of the flower and the fruit, but 

 in all probability determining the sex itself. 



6. The Influence of the Sea upon Plant Forms. It will be 



seen that quite as remarkable changes come to the sea as 

 to the desert plants, and in truth based upon similar 

 reasons. 



(i) Let us first consider the water supply. You will readily 

 bring before the mind's eye the picture of desert plants, which 

 represent in their modifications a lack of water. But you will 

 not so easily call to remembrance plants which have undergone 

 changes from an oversupply of water. Yet there are many of 

 them even in your own neighborhood. 



The Bald Cypress (Taxodium disticJium} grew in the present 

 Arctic region before the Glacial Epoch, in company with oaks, 

 maples, willows, the Redwoods (Sequoia gigantea, S. semper- 

 virens), the Gingko tree (Salisburia adiantifolid), Torreya, and 

 Glyptostrobus. During later changes in climate these trees 

 were driven from their home and travelled down widely different 

 lines into the South. For reasons which we are unable to 

 understand, the Sequoia, or Redwood, descended along the 

 California coast, the Glyptostrobus and the Salisburia or Gingko 

 tree, down the coasts of China and Japan, the Torreya and 

 Taxodium, or Cypress, to the eastern and southern parts 

 of North America. At present the Bald Cypress, to which I 

 wish especially to call attention, grows only along the water- 



