Some Questions which they Suggest. 27 



their sporangia, and that no one law is applicable to them 

 all ; but in all cases the sporangia appear to stand vertically 

 to the plane on which they grow. 



If we examine the trunk of an oak, we find an elaborate 

 structure of hard parts which maintains the tree in its 

 upward growth, and by the force of cohesion resists and 

 overcomes the force of gravity drawing it downwards. 

 If we examine the stalk of even a delicate flowering 

 plant, we find that it is constituted of cells, and that the 

 cell walls, as well as the fibres, afford to the stem a 

 certain amount of support ; but in the naked protoplasm of 

 the myxie we have no woody tissue, no cell wall, and yet 

 this, too, lifts itself away from the earth and towards the 

 sun and the air. We then see that the upward motion of 

 plants does not depend on cell walls, but is an inherent, an 

 original capacity of some protoplasm. 



We can easily appreciate the advantage which this 

 upward tendency gains for the organism, for it lifts it into 

 the air and exposes it to the influence of light. We know 

 the great results on the surface of the earth of this so- 

 called negative geotropism. If all plants had crawled 

 along the ground like the thallus of Marchantia or the 

 hyphoa of some fungi, we should have had a keener com- 

 petition for surface space even than now exists, and we 

 should have lost the beauty with which the earth's surface 

 is clothed. In the myxie lifting up its sporangia, we can 

 see in the small and in its simplest and most primitive 

 form, the existence of the same power which enables the 

 sequoia or the eucalyptus to lift themselves to such enormous 



