Leaves of Humulus lupulus possess two types of glandular trichomes: -peltate (lupulin) and bulbous. Peltate trichomes are formed from a protodermal cell by two anticlinal divisions in perpendicular planes, followed by two periclinal ones that give rise to the initials of the head cells, the basal and the stalk cells. Head cells divide successively in radial and irregular planes. Fully developed peltate trichomes are built of a glandular head consisting of 30 to 72 cells, four stalk cells and four basal cells. Bulbous trichomes are also formed from a protodermal cell by an anticlinal division followed by two periclinal ones that produce the initials of the glandular head cells, and the basal and stalk cells. Fully developed bulbous trichomes consist of four (occasionally eight) head glandular cells, two stalk cells and two basal cells. The density of peltate trichomes decreases with the expansion of the leaves. Both peltate and bulbous trichomes secrete essential oils. Peltate trichomes are the preferential site for the synthesis of bitter resins. Tannic acids could not be detected histochemically either in peltate or in bulbous trichomes. Both types of trichomes produce secretion that accumulates in the subcuticular space, being released, in the case of bulbous trichomes, by rupture of the cuticle.

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The composition of the essential oil isolated from Achillea millefolium L. ssp. millefolium cell suspension cultures was analysed by GC and GC-MS. The yield of the oil obtained by hydrodistillation or a simultaneous distillation -extraction of these cultures, harvested at days 8 -10 (end of exponential phase), was 0.001% (w/w). The analysis of the volatiles showed the presence of thirteen components; monoterpenes amounted to 5%, sesquiterpene hydrocarbons attained 40%, while eugenol, demethoxyencecalin and two unidentified compounds amounted to 45% of the total oil. Several methods were tested in an attempt to increase the essential oil production by the cultures: growth on solid medium, growth in light, use of a different culture medium, elicitation with cellulase or yeast extract, and growth in a two-phase system. Of the different methods tested, the growth in B5 + medium with Miglyol 812 led to the highest essential oil yield (0.002%, w/w), and resulted in a more diverse oil composition.

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SUM .VI A R YInfected roots of Ophrys Intea present numerous peroxisome profiles identified by diaminobenzidine (DAB) staining. The presence of uricase in these peroxisomes could also he recognized cytochemically. The activities of catalase and uricase, assayed using a crude fraction of peroxisomes, reached 0-8//kat min ' mg protein^' and 1-73 nkat min ' mg protein ' respectively. The role of uricase in purine metabolism is discussed in terms of host/ endophyte interactions in O. lutea mycorrhizas.