Revieic of Elements of Botany. 423 



have no room for extracts, but the following few words from the 

 chapter on nutrition may be interesting to our readers. 



'' Hygroscopicity, or the property of absorbins^ or giving out moisture 

 according to tlie nature of the body and the state of the surrounding at- 

 mosphere, is a property common both to organized and unorganized 

 matter. Young- tissues which are not filled up with foreign substances, 

 are most active in taking up moisture; thus the spongelets of roots are 

 eminently hygroscopic — the bark much less so. Sap-wood absorbs 

 readily. Young branches of willow or poplar stuck in damp soil will 

 take up sufficient moisture to keep the branch alive until new roots are 

 formed. Heart-wood, on the contrary, being filled with solid matter, is 

 not hygroscopic; hence it is more durable as timber, especially when 

 exposed to humidity. 



" But the absorption of moisture is controlled by a very remarkable 

 power, lately discovered by M. Dutrochet, a distinguished French physi- 

 ologist, called Endosmosis. This power undoubtedly exercises an im- 

 portant influence in vegetable physiology, as well as elsewhere. The 

 general rule in respect to its operation is, that if two fluids of unequal 

 density be separated by a membrane, even destitute of visible pores, the 

 lighter fluid passes through the inembrane, mingling with the denser. A 

 simple experiment will illustrate this. If a short tube or phial, with the 

 bottom broken off, be covered at one end with any vegetable or animal 

 membrane, nearly filled with a solution of cum arabic and half im- 

 mersed in water, the denser mucilage will attract the water through 

 the membrane, and the tube will be filled. A small portion of the denser 

 fluid also passes onward, and mingles with the water, but the prepon- 

 derance is greatly in favor of the mucilage, and the denser the fluid, the 

 stronger its attraction upon the water. Let the experiment be reversed, 

 by filling the tube with water and immersing it in a vessel of mucilage, 

 when, in accordance with the same rule, the water will slowly sink in 

 the tube, which will at length nearly empty itself. 



"This power offers a ready explanation of many acts of vegetable 

 life which were formerly altogether inexplicable. Several instances 

 will be adverted to in due time. We may here adduce a single illus- 

 tration, viz. the growth of fruits. When a fruit, such as the peach or 

 plum, begins to enlarge, its cells are filled with a fluid denser than the 

 sap ; by the property of endosmosis, therefore, they attract a large 

 portion of the neighboring sap into the fruit, which in consequence be- 

 comes juicy. The density of the fluid is kept up by the continual 

 evaporation of its watery portion, and thus the fruit is enabled to ap- 

 propriate a great part of the food of the plant, which it changes into a 

 pulp. In this, no doubt, we have also the true explanation of the fact 

 that plants are weakened and their growth checked by bearing fruit; 

 and that plants which flower but once (annuals and biennials), die for 

 the most part soon after the maturation of their fruit." (p. 105.) 



When we mention that, with the exception of Professor Tor- 

 rey's edition of " Lindley's Introduction to the J^atural System^^^ 

 this is the only work in w^hich the modern views of the eminent 

 physiologists of the day are brought forward in an American pub- 

 lication, we only announce how far in the rear we are in botani- 

 cal knowledge, and at the same time confess how much room 

 there is for improvement in the systems of teaching this science, 

 pursued in our places of instruction. We hope to see Dr. 



