105 CELLULAR TISSUE. 



in the shape of knobs. This fills one-half, two-thirds, or often almost the whole df the 

 cell-cavity. This thickening of the membrane contains (besides a compound of Silicon) 

 a large quantity of calcium carbonate, partly as a homogeneous infiltrated mass, partly in 

 the form of very small granules, or often of splitting crystalline masses. Examples, 

 Cerinthe aspera, major, minor, Onosma stellulatum, arenarium, Echium vulgare, fruti- 

 cosum, Lithospermum oflicinale, Anchusa italica, Helianthus tuberosus, trachelifolius, 

 macrophyllus W., Obeliscaria columnaris, Heliopsis Ixvis^ In the multicellular hairs of 

 Helianthus similar thickenings often occur in the lowest cell, both laterally and on the 

 under surface of the upper wall. Whether the silica-containing rosettes of cells in 

 Ulmus, Dillcniaccx, and Chrysobalanea; (Von Mohl, I.e.) which surround the hairs or 

 rudiments of hairs, and resemble the above, also contain calcium carbonate, is not 

 stated. 



In the hairs of many Cruciferx, — Alyssum, Cheiranthus Cheiri, Capsella, &c. — the. 

 presence of calcium carbonate in very large quantity is shown by reagents. It does not 

 occur as single distinguishable particles, but is contained mainly (or wholly?) in the 

 outer layers of the membrane, especially in the wart-like thickenings which protrude 

 outwards (comp. Fig. 21, D, p. 59). These appear on the fresh hair mounted in water 

 as strongly refractive, blueish and bright, after solution of the lime-salt very pale and 

 transparent. 



Also other strong hairs (Borragineae, Helianthus) appear to contain large quantities of 

 calcium carbonate in their lateral walls. 



Sect. 23. Incrustations of Lime. Calcium carbonate is often found in finely 

 granular masses, deposited, as an incrustation, upon the outer surface of the cuticle. 



(i) On the epidermis above the ends of the vascular bundles of many land 

 plants. On these spots lies a white granular scale of lime. This is the case in many 

 Fern leaves : Polypodium subauriculatum, meniscifolium, repens, aureum, sporado- 

 carpum, areolatum, crassifolium, morbillosum, &c., species of Nephrolepis, Aspidium 

 leucostictum, albopunctatum, pedatum, Lomaria attenuata "-, and on the leaves of the 

 white incrusted species of Saxifraga'. The above-named Ferns show at definite 

 points on the upper surface of the leaf shallow, in Lomaria attenuata deep, flask- 

 shaped depressions, in which, when the definitive development of the leaf is attained, 

 there appears the white scale of lime, which is not renewed after removal. Also in 

 the Saxifrages the lime scales are excreted in depressions, which lie on the upper 

 side of the leaf — in the species of Euaizonia on each of the marginal teeth, which 

 are covered with short blunt hairs — in S. caesia, 4-6, in pairs on the two margins, 

 and a single one at the end of the middle nerve: in S. retusa and oppositifolia 1-3-5 

 on the upper side. The depressions are filled up with the mass of lime : their epi- 

 dermis is distinguished from that of the rest of the leaf-surface by the small size and 

 thin walls of the cells rich in granular protoplasm, which in Lomaria attenuata grow 

 out as papilliK. Stomata are absent in the depressions in the above Ferns (Mette- 

 nius), in the Saxifrages the water-stomata described p. 53 are always present. 



(2) On the leaves and herbaceous stalks of Plumbagineae * (species of Plumbago, 



1 Compare von Mohl, I.e. p. 227. 



^ Treviranus, Verm. Schriften," IV. p. 66. — Mettenius, Filices horti Lipsiensis, pp. 8, 9. 



3 Unger, Einfliiss. des Bodens, &c.< p. 178.— The same, Beitr. z. Bhysiol. d. Pfl. VIII.— Sitz- 

 ungsbr. d. Wiener Acad. Bd. 43. p. 519.— Mettenius, I.e. 



* Braconnot, Ann. Chim. et Phys. LXIII. p. 375. — Treviranus, Physiol. II. p. loi. — Mettenius, 

 /. e. p. 9. 



