348 



inches in circumference, has been completely killed in a circular ring 

 seven inches wide, and the organs of vitality again restored, without 

 apparently affecting the health of the tree, which is now, while I write 

 (June, 1851), in full bloom. The results, T conceive, rather than add- 

 ing confirmation to the established theory, bear out Dr. Schleiden's 

 views in a remarkable manner. It is true, the newly -formed tissue 

 extended from the upper lip of the cut chiefly in the downward direc- 

 tion, and that very little appeared on the lower lip. But the train of 

 reasoning I adopt from these circumstances is that of Dr. Schleiden. 

 The flow of sap by endosmotic process from cell to cell, was inter- 

 rupted by the alburnum and cambium being cut across on the pillar 

 which was laid bare. It therefore diverged laterally, and followed its 

 natural upward course, on the three pillars where no laceration had 

 been made, which accounts for no growth taking place on the lower 

 lip. On the portion of stem above the cut, a greater degree of forma- 

 tive energy accrued, in consequence of the interruption the endos- 

 motic process met with below. The tissue thus formed would rather 

 extend itself on the vacant space under, i. e., the bare pillar, than 

 upwards, where endosmosis was less vigorous, in consequence of 

 many of the cells being filled with sap of greater density. In this 

 manner it continued to grow until it reached the lower lip of the cut, 

 where its downward course was obstructed, when it spread in a latei-al 

 direction over the surface of the lip, as well as upwards, until the bare 

 surface became covered over. During the whole process it did not 

 occur to me that the young wood was formed by a i-eturning bark-sap. 

 The growth seemed gradual and not periodical. The young tissue 

 taking a lateral and upward direction when it met the lower lip, shows 

 that, although the tendency be downwards, it will alter. 



A remarkable example of the permeability of the tissues of plants 

 has further been proved through this experiment. From knowing the 

 heart-wood was dead at the part of the stem which was operatod on, 

 I was desirous to ascertain whether it continued so to the apex of the 

 tree, which I had some reason to suppose it did, from having, about 

 four years ago, observed a small portion of the top shoot dead. I, 

 however, found the heart-wood full of sap, and apparently very healthy, 

 in a piece of the top shoot which I had lately cut from below the 

 dead part. 



With similar objects in view, a second series of experiments have 

 been made, at various times within the last twelve years, by planting 

 cuttings of free-growing plants with their tops downwards. Placed in 

 this way, adventitious roots were protruded, aud tiie plants grew. 



