MICROSCOPIC OBJECTS. 



Fig. 7. Transverse Section of the Stem of the Water 

 Plantain (Alisma plantago), x 30, Endogen. 



This section of the stem of the Water Plantain has been 

 drawn especially to illustrate the extremely loose form in 

 which the air-passages are often found. They are divided 

 horizontally by membranous partitions, some of which are 

 seen in the figure. These are composed of minute cells, with 

 short processes and intervening air-spaces, somewhat resem- 

 bling the structure met with in the Rush. 



This section is best mounted in liquid. 



Fig. s. Transverse Section of Elder -pith (Sambucus nigra), 



x90. 



This section shows the pitted membrane which forms the 

 cells. The pitted appearance is caused by an irregular for- 

 mation of the secondary deposit. Although the pits may 

 seem to be holes in the membrane, on the application of 

 sulphuric acid and iodine they will be found to be coloured, 

 as well as the surrounding tissues, which would not occur if 

 they were holes. Membrane is sometimes thickened by a 

 dense deposit, so as to have nearly the appearance of bone 

 (see fig. 18 &c.). 



This pith (Elder) is often used by microscopists to clean 

 their object- and eye-glasses. 



It may be mounted dry or in liquid. 



