fi'2 



SUGGESTIONS FOR LABORATORY WORK. 



vessels in the primary xylem, but none in the secondary, 

 the latter being almost entirely made up of the cells with 

 bordered jnfs, already described. 

 The bundles of the leaves are continuous with bundles in the 

 stem. Leaves appear at first as protuberances on the 

 side of the stem close to the growing point, and the upper 

 ends of the primary bundles almost at the very beginning 

 bend outwards towards the new leaves, the lower part 

 being continued down the stem. In the monocotjledons 

 these bundles first arch inwards to'wards the centre of the 

 stem, and then outwards and downwards, thinning out 

 as they descend. Hence, in a cross-section (Fig. 281) the 

 bundles appear more crowded towards the circumference, 

 and also smaller. Such a stem is, therefore, found to be 

 harder at the outside than at the centre. 



LABORATORY WORK WITH THE MICRO- 

 SCOPE. 



Practical Suggestions. 



It is assumed that the teacher will give all necessary in 

 structions as to the manipulation of the microscope, preserva- 

 tion and hardening of material, section-cutting and mounting, 

 so that it will only be urged here that as the one object in view 

 is to obtain a knowledge of plant-structure as exhibited in the 

 living organism, the simplest methods are almost invariably the 

 best. All the necessary section-cutting can be done with a good 

 razor, and water will nearly always serve as a mounting medium, 

 when fresh material is used. 



The Cell. As a suitable object to begin with in the study of 

 the vegetable cell. Professor Bower recommends the com- 

 mon Spirofjyra which so frequently forms a green scum 

 on the surface of ditches and slow-flowing waters. It is 

 made up of unbranched threads irregularly matted to- 

 gether, and can generally be easilj' recognized. A small 

 portion of the living plant should be mounted in water in 

 the usual way, and studied first with a low power, when 

 the following points can be observed and drawings made 

 of them : 



(a) The cell-wall which forms the lateral limit of 



each thread. 



(b) The cross-walls which divide the threads into cells. 



(c) The protoplasmic contents of each cell, with the 



green chlorophyll granules which here form 

 .'Spiral bands. 

 With a liigher power try to make out : 



(a) the film-like lining of each cell {primordial 



utricle). 



