Page 62 – Trichomes


Page 62 – Trichomes



c. 1940



Fig. 55 . Trichomes. Outlines of the trichome heads (in A), and trichome heads and stomata (in B; the larger circles are the-trichomes) as they occur on the abaxial surface of a young, i.e., prechlorophyllaceous, leaf from the center of the leafy terminus of the stem (the so-called "crown" or "top"). In A, the bottom of the drawing represents the lower limit of the region (i.e., youngest) in which the trichomes form (no furrows and ridges have yet formed in this youngest portion, about 1-1.3 cm. from the extreme base of the leaf). In B, a region above that shown in A, where the stomata are visible; the latter and the trichome heads are shown in outline. Notice the alignment of the stomata and trichomes in the furrows, and the relative number of each. Circles represent the actual outline s of these two epidermal structures; the epidermal cells are not shown. X100. C, surface views of selected portions of the adaxial epidermis at the upper limit of the basal (i.e., non-chlorophyllaceous) region of a young leaf of a 6-months-old plant to show the stages of development of a trichome head of the scutiform type. The trichome heads illustrated occurred at the following distances from the very base of the leaf: 1, 1.2 mm.; 2, 1.4 mm.; 3, 1.8 mm.; 4, 6.6 mm.; 5, 6.9 mm. X340. D. Two series of trichome heads, 1 and 2, from the adaxial epidermis of a young leaf of a 6-months old plant to show the stages of development of a trichome head of the irregularly-shaped types shown in Figs. Broken lines show the cross sections of the trichome stalks. X340.