OBSERVATIONS UPON THE PHENOMENA OF PLANT-LIFE. IJ17 



apple trees early in the spring, covered with blossoms in a similar way while 

 l}'ing on the ground. 



It is a well established fact that the roots of most woody plants have not 

 power at any season to force water to any considerable hight wheu separated 

 from their stems. Upon this point a large number of observations have been 

 made, which will be described in another place. 



THE EOOTS 



of all plants growing on ordinary soil develop most freely and absorb most 

 abundantly wlien the earth is well drained and aerated. Thus we find that 

 the crude sap imbibed by the root-hairs from the surface of the particles of the 

 soil seems to be taken up in a dry state, that is, it appears to be absorbed mole- 

 cule by molecule, no fluid water being visible, and carried in this form through 

 all the cellulose membranes between the earth and the leaf, by which it is to 

 be digested or exhaled. We do not say this is literally true, but it accords very 

 nearly with what is constantly to be seen in some species of plants. The cir- 

 culation of the sap in a poplar tree is very dry compared with that of the blood 

 of any animal. Not a drop of moisture will ever flow from the wood of an aspen, 

 so far as we have observed. Nevertheless, it grows very freely and st irts very 

 early in the season. 



THAT LIVING CELLULOSE 



has a peculiar and very powerful affinity for water is evident from the experi- 

 ments of De Vries, who discovered that when a shoot of an herbaceous plant 

 with large leaves is cut, and the fresh surface allowed to come for a short time 

 into contact with the air, it loses much of its absorbing power and the leaves 

 wilt. If, howeyer, the section be made under water, so that the living tissue 

 is not exposed to the air, its power of imbibition remains unimpaired, and the 

 leaves do not wilt. 



SOLID SAP. 



It appears, therefore, that much of the crude sap passes through the mem- 

 branes of the sap-wood or woody fibre or cellular tissne of plants in an appar- 

 ently solid form, combined with the cellulose, just as the water in dry slacked 

 lime or a plaster cast is in a solid form. In all these cases it may be obtained 

 as a liquid by distillation at a temperature of 213° Fahrenheit. The cause of 

 the motion seems to be the removal of the water from the tissue at some point 

 by exhalation, by chemical combination, or by assimilation. Whenever any 

 portion of the living cellulose has an insufficient amount of water to saturate 

 its affinity, it imbibes an additional quantity, and this process is continued 

 from cell to cell downward, or backward to the roots and the earth. 



THE CONDUCTING POWER 



of the cellulose of sap-wood is very remarkable, as is seen in the fact that when- 

 ever a limb of an apple or peach tree breaks down under its burden of fruit, it 

 very rarely wilts or fails to ripen its crop. Those who have compared the area 

 of a section of the trunk of a large tree with the area of a section of its branches 

 at any point above, must have noticed that the relative amount of sap-wood 

 rapidly increases as we ascend toward the top, the young twigs and branches, 

 containing no other wood. 



AN" ELM IN AMHEKSTj 



famous for the beautiful symmetry of its form, and known as the Ajres elm, 



