THE TISSUES OF PLANTS. 29 



In the latter the bundles lie adjacent to the thick dark bauds of fibrous 

 tissue. 



(/) The tracheids of Conifers (pines, spruces, etc.) make up very 

 nearly the wliole bulk of the wood of tliese trees. Make a longi- 

 tudinal radial section of a pine-twig by the method employed in 

 studying fibrous tissue (IV. a, above). Note that the tracheids bear 

 some resemblance to the wood-fibres of other wood. However, their 

 large round bordered pits are characteristic. 



{g) Make longitudinal tangential sections of the same twig. Note 

 that the bordered pits are not seen (except in section) in specimens so 

 made. 



(Ji) Make cross-sections of the same twig and note that the tissue is 

 homogeneous. Compare with a similar section of an oak-twig, and 

 note the absence in the pine of the large pitted vessels which are so 

 well shown in the oak. 



(i) Make very thin longitudinal radial sections of the wood of hack- 

 berry. By careful examination tracheids may be found resembling 

 the wood-fibres, but marked with fine spirals. 



{]) Similar traclieids may be found intermingled with the wood- 

 fibres of other trees, as the maple, box-elder, elm, etc. 



53. Tlie Primary Meristem. — Under this n^me are 

 grouped tiie unformed and growing tissues found at the 

 ends of young stems, leaves, and roots. In these parts the 

 tissues described above (paragraphs 36 to 52) have not yet 

 formed; they are, on the contrary, composed entirely of a 

 mass of thin-walled, growing, and dividing cells contain- 

 ing an abundance of protoplasm. In the lower plants the 

 meristem-cells do not change much in their configuration 

 or general structure as they develop into the ordinary 

 plant-cells; but the higher the type of plant, the greater 

 are the changes which take place during the development 

 of meristem into permanent tissues. 



54. In most plants aside from the flowering plants the 

 primary meristem is the result of the continually repeated 

 division of a single mother-cell situated at the apex of the 

 growing organ. In the simplest forms this apical cell 



