36 PRACTICAL BOTANY 



It will be apparent that in the internodes the bundles run 

 parallel to one another, and as a rule without lateral fusion. 

 This regularity is disturbed at the nodes by lateral fusions 

 of some but not of all of the bundles, and by the entry of 

 fresh bundles from the leaves (usually three from each leaf), 

 into the vascular ring. 



IV. In a longer piece of the stem follow carefully the course 

 of several of the bundles entering from the leaves, as far as they 

 can be traced independently and without fusion. This will be 

 possible at least for one internode, and usually for two or 

 three ; but the distance through which this independent course 

 can be traced is variable in this plant. Further, the lateral 

 fusions do not occur only at or near the nodes ; instances may 

 not unfrequently be found of fusions occurring at various points 

 in the internodes. 



For further description of the rough anatomy of the Sunflower, 

 and of the vascular system in other herbaceous Dicotyledons, 

 see larger edition, pp. 57-61. 



Microscopic Observations. 



The material should be kept in spirit for some time, to 

 remove resin and air, and to harden the tissues ; but this is 

 not indispensable, and fresh material may be used, though it is 

 not so satisfactory. 



I. Cut -thin transverse sections of a stem of a well-grown 

 plant of Helianthus, i.e. of a stem more than half an inch at 

 least in diameter. 



Mount some of these in glycerine or glycerine jelly (these 

 may be kept as permanent specimens), and others in chlor- 

 zinc-iodine. Examine these first with a low power, and ob- 

 serve the following tissues in succession, starting from the 

 exterior : 



i. The epidermis, a single peripheral layer of cells, not very 

 well defined from the underlying tissues-: it completely covers 

 the surface. 



The margin is not perfectly regular, but is here and there 

 extended outwards at the regions surrounding the bases of the 



