liuing When viewed by transmitted light, it appears as if 

 ridtUed full of holes. ? 



a. It is oftitw'o kinds j'-^st, mticulatcd, having its tubes intenitpted by joints and 

 partitions, as in the oali, \-ine, and in the monocotyledonous stemsV^d, continuous, 

 without joints or partitions ; often found in tlie roots of pbnts.- 



b. These are the hirgest vessels in the vegetable fabric ; and then- open mouths 

 are pai-ticularly discernible in the cuttings of the oak, cane, &c. It is tlirough 

 these that the sap arises to the stem, and is conveyed to the leaves. 



33. Vascular TissuEConsists essentially of spiral vessels, with 

 their modifications?} 



a. The true spiral vessel much resemblesrthe woody fibre in 

 form, being a long, slender tube, tapering each ^v-ay, but is tliin- 

 ner and weaker^ Its peculiar mark is an elastic, sphal fibre, 

 coiled up within it, from end to end. 



b. The spiral thread is usually single, sometimes double, triple, &c. In the 

 Cliinese pitcher plant, it is quadniple. (Fig. 1,/) 



c. In size, spiral vessels are variable. Generally their diameter is about yJLg- 

 of an inch ; often not more than ^ o'oo - 



d. Tlie situation of spiral vessels is in the medullary sheatli, that is, just around 

 the pith ; also in eveiy part which originates from it, such as the veins of leaves, 

 petals, and other modifications of leaves, and especially in the petioles, from 

 which it may be uncoiled, in the manner above desciibed. (28, a.) 



e. In their perfect state they contain ah*, which they transmit, m some way, 

 from one to another. 



/.- Ditcts are membranous tubes, with conical or rounded ex- 

 tremities, their sides being marked with transverse bars, rings, 

 or coils, incapable of bemg um:olled without breaking.') # 



FIG. 2. — Forms of tissue, &c. ; a, annular ducts; 5, spiral and annular at intervals; c, 

 iaticiferous tissue ; e, stomata of iris — vertical section, rf, d, green cells at the orifice ;/", yj 

 cells of the parenchyma, e, air-chamber ; g-, g, view of epidermis and stomata of yucca, k, 

 sJoaata closed ; small, luminous bodies in the cells. 



