14 STUDIES IN HISTOLOGY. 



made at different points in the organ, care being taken to arrange 

 the sections in their proper sequence. 



The following material will be useful for practice in the deter- 

 mination of the course of the bundles : young shoots of Clematis, 

 Vitis, and Phaseolus (all dicotyledons) ; and, after these, shoots 

 of Spiderwort, the rootstock of Convallaria (Lily of the Valley), 

 or of Smilacina, and if possible the bud of a young palm. 



The course of the bundles in leaves and dry fruits can be 

 easily demonstrated by " skeletonizing" them. This is effected 

 by keeping the leaves for a long time in a dilute solution of 

 calcic hypochlorite (see 50). 



DEVELOPMENT OF THE ELEMENTS. 



This must be examined in the youngest seedlings of the plants 

 now spoken of. The sections must be through the growing 

 points, and should be well cleared b}' one of the processes de- 

 scribed in 16 or 24. For the development of special structural 

 elements, for example latex-cells, see Part I. 



HISTOLOGY OF THE VARIOUS ORGANS. 

 I. THE ROOT. 



The student ma}- use, for demonstration of the histology of 

 the root-tip, any seedlings which have been grown either in water 

 or on a clean support, and are therefore free from grains of 

 earth. Root- hairs are best examined on seedlings sprouted upon 

 moist sponge or bibulous paper. 



II. THE STEM. 



It is advised that the student now prepare, in addition to the 

 sections of stems previously examined, sections through two and 

 three year old shoots of any common dicotyledon, and note all 

 differences which exist between the different wood}' elements 

 forming the rings, and all changes in the bast. The growth of 

 cambium should be carefully examined in the young shoots of 

 Pine and of Oak. 



For the study of the secondary changes in the bark, the 

 twigs of black currant or of white birch afford good material, 

 the successive changes being easily followed. 



The occurrence of true cork in out-of-the-way places is illus- 

 trated by Catalpa, Professor Barnes reporting that it sometimes 

 occurs between the annual layers in the stem of Catalpa speciosa. 

 Other cases should be looked for. 



