1884.] LAWS OF GBOWTIL 285 



1, The primary direction of growth, above the collar of a tree, is 

 upwards. 



1. Light attracts growth in the direction of the horizon, as well as 

 in the direction of the zenith. 



o. Terrestrial gravitation acts in opposition to light on growing 



parts. 



4. Shade and lack of moisture are inimical to growth. 



5. Cold and concussion destroy growth. 



Proof of the first of these laws has been given in our germination 

 experiment. I'roof of the second law may be had from many sources. 

 That light attracts growth horizontally is well known to growers of 

 plants in what are called ' lean-to ' greenhouses. I'lants grown in 

 such houses require to be frequently turned on their stages to prevent 

 a one-sided or listed development. Our third law, which declares 

 that terrestrial gravitation acts in opposition to light on growing 

 parts, is well exemplified in the Pine family of trees. Trees of this 

 family are remarkable for the horizontal disposition of their branches. 

 If, however, you examine the top shoot of a young Pine when groAvth 

 is inactive, i.e., during the hibernating season, you will see that the 

 buds at the extremity of the shoot are all disposed in an upward 

 direction. If you will further examine this shoot after the hibernating 

 season has passed, and when the buds have started into growth, you 

 will see that the growths from all the buds — stem and branch buds 

 alike — take an upward posture. Till these tender shoots have 

 attained a length of several inches, gravity does not seem to affect 

 their posture, because they are still all but perpendicular, the only 

 safeguard at all times against gravitative disaster. At this stage a 

 most interesting phenomenon is presented. The delicate young 

 leaves that cover all the shoots begin to spread themselves out in 

 obedience to the promptings of the light that surrounds them. This 

 expansion of the leaves of all the shoots gives rise to a pressure for 

 space at a point above that where all the shoots converge. At this 

 point the pressure is nearly equal all round the central or stem shoot, 

 which is thereby kept in equipoise while all the others are pushed 

 apart far enough to secure the necessary space for all. Gravity now 

 acts effectively upon these branch shoots, and in due time they are 

 compelled to take that posture which is characteristic of all Pine trees, 

 a posture which describes nearly a right angle with the trunk. It is 

 not too much to affirm that to this apparently unimportant fact is 

 due, in great measure, the great timber capabilities of the Pine family 

 of trees. In a word, it redeems them from shrubbiness. ' Very won- 

 derful ; can it be so ? ' Well, it is not to be given credence to because 

 I have said it, or because, probaToly, I am the first to state it. To assure 

 ourselves of its truth let us go to another Pine tree whose top 



