CHAPTER III. 



HOW PLANTS OBTAIN WATER. 



In connection with the study of the means of absorption from the soil 

 or water by plants, it will be found convenient to observe carefully the 

 various forms of the plant. Without going into detail here, the suggestion 

 is made that simple thread forms like spirogyra, oedogonium, and vau- 

 cheria; expanded masses of cells as are found in the thalloid liverworts, 

 the duckweed, etc., be compared with those liverworts, and with the mosses, 

 where leaf-like expansions of a central axis have been differentiated. We 

 should then note how this differentiation, from the physiological stand- 

 point, has been carried farther in the higher land plants. 



45. Absorption by Algae and Fungi. In the simpler forms of plant life, 

 as in spirogyra and many of the algae and fungi, the plant body is not dif- 

 ferentiated into parts.* In many other cases the only differentiation is 

 between the growing part and the fruiting part. In the algae and fungi 

 there is no differentiation into stem and leaf, though there is an approach 

 to it in some of the higher forms. Where this simple plant body is flat- 

 tened, as in the sea-wrack, or ulva, it is a frond. The Latin word for 

 frond is thallus, and this name is applied to the plant body of all the lower 

 plants, the algae and fungi. The algae and fungi together are sometimes 

 called the thallophytes, or thallus plants. The word thallus is also some- 

 times applied to the flattened body of the liverworts. In the foliose liver- 

 worts and mosses there is an axis with leaf-like expansions. These are 

 believed by some to represent true stems and leaves, by others to represent 

 a flattened thallus in which the margins are deeply and regularly divided, or 

 in which the expansion has only taken place at regular intervals. 



In nearly all of the algae the plant body is submerged in water. In these 



* See Chapter 38 for organization of members of the plant body. 



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