THE TISSUES OF PLANTS. 29 
In the latter the bundles lie adjacent to the thick dark bands of fibrous 
tissue. 
(f) The tracheids of Conifers (pines, spruces, etc.) make up very 
nearly the whole bulk of the wood of these trees. Make a longi- 
tudinal radial section of a pine-twig by the method employed in 
studying fibrous tissue (IV. u, 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 sectious of the same twig. Note 
that the bordered pits are not seen (except in section) in specimens so 
made. 
(h) Make cross-sections of the same twig and note that the tissue is 
homogeneous. Compare with «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. 
(f) Similar tracheids may be found intermingled with the wood- 
fibres of other trees, as the maple, box-elder, elm, etc. 
53. The Primary Meristem.— Under this name are 
grouped the 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 sim~lest forms this apical cell 
