Trichomes adaxial

FIGURE 4.5 Leaf and stem trichomes (A) adaxial surface, falcate and moniliform trichomes pointing toward the leaf apex (B) abaxial surface displaying falcate, moniliform, and glandular trichomes, the orientation of which is more random (C) glandular trichome found only on the abaxial surface (D) falcate and moniliform trichomes and (E) acuminate trichomes on an immature stem. 

Fig. 7-10. Leaf cross sections of Phaseolus vulgaris > hybrids of Populus sp., and Quercus palustris after one to several rainfalls of simulated acid rain of low pH. Fig. 7. Initial injury of epidermal cells near a trichome hydathode. Note injury is greatest at the anticlinal walls of epidermal cells at the base of a hydathode on P. vulgaris. Fig. 8. Initial injury of subsidiary cells near the guard cells of a stoma. The cells of the palisade parenchyma appear normal on P. vulgaris. Fig. 9. A large lesion with an injured adaxial epidermis, palisade parenchyma, and spongy parenchyma near vascular tissues in poplar. Fig. 10. A cross-section of a gall on a leaf of palustris. Note both collapsed epidermal and palisade cells. Hypertrophy and hyperplasia of spongy mesophyll cells are also evident.

Lesion development after acid rain exposure is localized. Lesions were localized initially near trichomes and stomata on adaxial leaf surfaces. Scanning electron micrographs showed that 15% of all lesions began at the bases of spiked and glandular trichomes while 20% originated at or near stomata. Very few (5%) lesions began in areas unassociated with these structures. 

The experimental results demonstrate that initial injury to foliage by simulated acid rain preferentially affects the leaf indumentum near trichomes and vascular tissues. Characteristics of the adaxial leaf surface are probably important after one or two rainfalls. However, after many rainfalls, in which epidermal cells are injured, other characteristics of the leaf may become important. In general, foliage of plant species that exhibits extensive hyperplastic and hypertrophic responses has less injury than foliage of species that have these two responses. In this manner, the hyperplastic and hypertrophic responses of foliage may alleviate extensive foliar injury. 

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