150 BOTANY. 



outer coat, and provided with a peculiar, whitish, spongy appen- 

 dage attaching it to the placenta. A longitudinal section of a 

 ripe seed (K) shows the very small, nearly triangular embryo 

 (em.), while the rest of the cavity of the seed is filled with a 

 white, starch-bearing tissue, the endosperm. 



A microscopical examination of the tissues of the plant shows them to 

 be comparatively simple, this being especially the case with the fibro- 

 vascular system. 



The epidermis of the leaf is readily removed, and examination shows 

 it to be made up of oblong cells with large breathing pores in rows. The 

 breathing pores are much larger than any we have yet seen, and are of 

 the type common to most angiosperms. The ordinary epidermal cells are 

 quite destitute of chlorophyll, but the two cells (guard cells) enclosing the 

 breathing pore contain numerous chloroplasts, and the oblong nuclei of 

 these cells are usually conspicuous (Fig. 82, G). By placing a piece of the 

 leaf between pieces of pith, and making a number of thin cross- sections 

 at right angles to the longer axis of the leaf, some of the breathing pores 

 will probably be cut across, and their structure may be 'then better under- 

 stood. Such a section is shown in Figure 82, /. 



The body of the leaf is made up of chlorophyll- bearing cells of irregular 

 shape and with large air spaces between (77, in). The veins traversing 

 this tissue are fibro- vascular bundles of a type structure similar to that of 

 the stem, which will be described presently. 



The stem is made up principally of large cells with thin walls, which in 

 cross-section show numerous small, triangular, intercellular spaces (i) at 

 the angles. These cells contain, usually, more or less starch. The fibro- 

 vascular bundles (C) are nearly triangular in section, and resemble con- 

 siderably those of the field horse-tail, but they are not penetrated by the 

 air channel, found in the latter. The xylem, as in the pine, is toward 

 the outside of the stem, but the boundary between xylem and phloem is 

 not well defined, there being no cambium present. In the xylem are a 

 number of vessels (<7, tr.) at once distinguishable from the other cells by 

 their definite form, firm walls^, and empty cavity. The vessels in longi- 

 tudinal sections show spiral and ringed thickenings. The rest of the 

 xylem cells, as well as those of the phloem, are not noticeably different 

 from the cells of the ground tissue, except for their much smaller size, 

 and absence of intercellular spaces. 



The structure of the leaves of the perigone is much like that of the 

 green leaves, but the tissues are somewhat reduced. The epidermis of 



