GRASSES 265 



may be hung from the middle point of each cylinder. 

 The result will leave no doubt as to the greater resistance 

 to bending of the hollow cylinder. 1 



The hollow-grass haulm is light, strong and springy, 

 yielding easily to wind, without being damaged by it, 

 except indeed when the seeds are nearly ripe, and the top 

 of the haulm is heavily loaded. Then wind and ram may 

 lay the haulms flat, but even for such an accident a remedy 

 is provided, as we shall shortly see. 



Solid partitions or knots mark the places where the 

 bases of the leaf-sheaths are attached to the haulm. Here 

 the vessels pass out into the leaves, arid it is chiefly the 

 interwoven vessels which form the knot. The solid 

 partitions stiffen the haulm, and hinder it from becoming 

 flattened by pressure. But there is another and less 

 obvious reason for the knots. 



Take an entire grass-plant fresh from the ground, and a 

 foot or more in height ; plant it in a tray of wet earth or 

 sand, not upright but horizontal, and see what will happen. 

 A very top-heavy grass will not do. If the experiment 

 is made with care and judgment, you will see in the course 

 of a day or two that the haulm begins slowly to erect 

 itself. Each segment between two neighbouring knots 

 sets itself at a small angle to the segment next below, 

 and as all the angles are bent towards the same side, the 

 horizontal stem soon begins to rise. Before long it will 

 be found to have completely erected itself, and perhaps 

 to lean over a little to the opposite side. You can hardly 

 fail to remark that all the bending necessary to erection 

 is effected at the knots, and that the intervening parts of 

 the stem are nearly straight all the time. There is evidently 

 at each knot what we may call an organ of movement. 

 (Compare clover and wood sorrel, pp. 125, 132.) If you 

 mark one of the knots with horizontal Indian ink lines pass- 

 ing round it a small distance apart (say I mm.), you will see 



1 For the reason of the different resistance to bending of the two 

 cylinders I may refer the reader to Round the Year, article "Hay-time." 



