EQUISETUM SPOROPHYTE 327 



serve to propagate the plant by a purely vegetative 

 process. Any node separated from the parent plant 

 may also serve the same purpose under favourable cir- 

 cumstances. 



7. Observe particularly that the teeth of each leaf- 

 sheath correspond in position to the channels of the 

 next higher internode : since the teeth are continuous 

 downwards with the ridges of the lower internode, 

 it follows that the ridges of the lower internode 

 alternate in position with those of the internode next 

 above it. 



Strip off carefully one leaf-sheath, and it may then 

 be clearly seen that the ridges of the upper internode 

 alternate with those of the internode next below it. 



Microscopic Investigation 



II. Cut transverse sections from a mature internode 

 of an upright aerial stem : mount some in glycerine, 

 others in chlor-zinc-iodine, and examine first with a 

 low power : observe 



i. The sinuous outline of the section, the projections 

 corresponding to the ridges observed externally with 

 the naked eye, and the indentations to the channels 

 intervening between them. 



ii. The section is limited at the periphery by an ill- 

 defined layer of epidermis, which, together with sub- 

 jacent tissues, forms a band of thick-walled tissue of 

 very variable breadth ; thus the band is broad at the 

 most convex part of the ridges, and at the most de- 



