. Physiological botany; I. Outlines of the histology of phænogamous plants. II. Vegetable physiology. Plant physiology; Plant anatomy. recent plants. When the wood in a pine stem is cut radially, the flattened sides of tiie wood-cells exhibit the dotted appear- ance seen in Fig. 60. The number and mode of distribution of the markings in the wood- cells or tracheids of Co- niferae are so nearly con- stant, that they may be used with considerable certaint}- in tlie discrimi- nation of a few genera. 269. In a transverse section of the mature tra- cheids the discoid mark- ings are plainly seen to
. Physiological botany; I. Outlines of the histology of phænogamous plants. II. Vegetable physiology. Plant physiology; Plant anatomy. recent plants. When the wood in a pine stem is cut radially, the flattened sides of tiie wood-cells exhibit the dotted appear- ance seen in Fig. 60. The number and mode of distribution of the markings in the wood- cells or tracheids of Co- niferae are so nearly con- stant, that they may be used with considerable certaint}- in tlie discrimi- nation of a few genera. 269. In a transverse section of the mature tra- cheids the discoid mark- ings are plainly seen to be pits having an arched border or incomplete dome, and it is also seen that the thin spot or pit is common to two contiouous cells. 60 Hence the two domes, being on opposite sides of a partition-wall, have a lens shape, and the central perforations are nearlj- or exactly opposite each other (Fig. 62). Even in the same Speci- men the bordered pits vary witliin com- paratively narrow limits both as regards tlie size of the disc and that of the central aperture. The two domes making up a single dis- coid marking are at first separated by a delicate plate of unequal thickness; but later this middle lamella maj^ be broken down, and then a free passage extends from one cell to tlie other. The character of the domes and the mid- dle plate can be understood from the ac- companying figures of sections of the stem of Pinus sylvestris (Figs. 62 and 63). According to Sanio, the sections should be boiled in acetic acid, in order to remove all cell-contents. Fig. 60. Ai-eolated or disciform markings of tlie wood-cells (tracliei'Js) of Pinus Xjariclo : a, aspect of radial walls; 6, a transverse section; c, development of tlie marldngs in Pinus sylvestris. (Sanio.) Figs. 61 and 62. Pinus sylvestris. Transverse sections of nearly perfect and perfect discoid markings. (Strasburger.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for
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