104 A BIT OF GROUNDSEL. 



tured (Plate XIL, Fig. 2), and the centre is left vacant, thus 

 affording an excellent example of how the stems of many plants 

 become hollow. 3. — The fibro-vascular tissue (Plate XIL, Fig. i 

 c and Fig. 2), in bundles more or less numerous, but where our 

 section was cut numbered twenty-six, and arranged with the 

 smaller and younger bundles alternating with the larger. Their 

 division into xylem or woody matter and phloem, or portions 

 wherein addition and increase take place by growth, is easily dis- 

 tinguished, without having resort to the double staining so need- 

 ful in many cases. 



The polariscope will afford much assistance in examining these 

 sections, and while noting the various arrangements and forms of 

 the cells, we shall find that the longitudinal section of a stem of 

 Groundsel is a much more beautiful polariscopic object than 

 dozens of the ordinary polarising slides. The sections made 

 while preparing this paper were cut slightly oblique with a razor 

 and mounted, for the time, in a few drops of water. The leaf did 

 not polarise at all. A transverse section showed an epidermal 

 layer of small cells, containing no chlorophyll (Plate XIL, Fig. 5). 

 This causes the slightly crystalline appearance of the upper side of 

 the leaves. Beneath this epidermal layer is a thickness of five or 

 six cells, full of chlorophyll, whose rounded form is owing to 

 freedom from compression. The under-surface of the leaf con- 

 sists of map-shaped cells, among which are the stomata opening 

 into large air-spaces (Plate XII.^ Fig. 6). A i-inch o.g. showed 

 the stomata very well. 



No crystals or lactiferous vessels could be discerned in the 

 stem or leaf, and no trace of starch appeared in any part of the 

 plant in answer to the iodine test. 



Under a ^-inch o.g., a root-fibre was a very interesting object, 

 having a canal in the centre (Plate XIL, Fig. 7), bordered by 

 spiral vessels continued to the root-cap, and was quite transparent 

 with ordinary light. 



On the leaves were found two species of fungi, Peroiiospora 

 gafigliformis (Plate XIL, Fig. 9), a white mildew, covering the 

 under side, the tips of whose branches are in an umbel, while the 

 spores are globular. Nothing can be more lovely than a colony of 

 this fungus, seen with a J-inch o.g., and Lieberkuhn. It is a 



