GERMINATION OF THE SEED 185 



pull of gravitation, which is up and which is down ; and (3) the 

 use of processes of growth in such a way as to bring the parts 

 around into the up-and-down position. A fair simile helping 

 to make the process clear is that of a sailor starting to cross 

 the ocean, steering by compass. Here, too, are the three 

 elements: (i) the sailor knows to what port it is to his 

 interest to go ; (2) he perceives by observation of the compass 

 which is the proper direction for him to take; (3) he so ad- 

 justs his mechanism of rudder and steam, or sails, as to take 

 him to his destination. The plant uses the pull of gravitation 

 as the sailor uses the compass, purely as an index to direction, 

 and gravitation no more pulls the plant into the up-and-down 

 position than the compass pulls the sailor north and south. In 

 both cases it is previous experience which gives the knowledge 

 of the proper direction to be taken ; in both cases there is use 

 of a guide to show which is the direction ; and in both cases 

 there is a motive mechanism to carry them into the advanta- 

 geous position. Later studies will prove to the students that 

 gravitation is not only used as a guide to the up-and-down direc- 

 tion, but also as a guide to lateral directions, as in lateral roots 

 and stems, and in many creeping stems and climbing roots ; 

 here, too, the analogy with the compass holds, for the sailor 

 need not go north or south as the needle points, but at any 

 angle between which it is his interest to take, and the compass 

 guides him as well east or west, though it points north and south ; 

 and this is true, also, of gravitation with the plant. The reason 

 why gravitation is used as a guide instead of light (by the 

 stems), or moisture, etc. (by the roots), which also would guide 

 those parts into the proper directions is, no doubt, this, that 

 gravitation acts in the proper direction, with constant intensity, 

 and at all times, while all of the other influences vary in direc- 

 tion, and are sometimes altogether absent. 



