SECONDARY THICKENING. NORMAL DICOTYLEDONS. 529 



sometimes they occur in relatively very small quantities, as in the inner zone of bast 

 of the Ladenbergia last-mentioned, and in the officinal barks of Cinnamomum, 

 Croton Eluteria\ Larix europsea ^ and JNIahonia Aquifolium. 



As the fibres are included in the general serial arrangement of the bast, it follows 

 that the more closely they stand, the more distinct in this case also are the inter- 

 rupted, radial, and concentric zones which they form, as e. g. in Cinchona macrocalyx, 

 figured by Berg, Lc, Taf, 35, and very beautifully in Laurus Sassafras. In general, 

 numerous intermediate cases occur between the forms of distribution enumerated 

 here and under 5, as was to be expected beforehand. In this respect the cortices of 

 Cinchonacese present an instructive series of gradations. Ulmus also deserves to be 

 again mentioned here. 



The appearance of s/ior/ sclerenchymaloiis elements isioiie-elevwiis) in the bast will 

 be considered in the next chapter, in order to avoid repetitions. 



Sect. 166. Sacs containing crystals are often a characteristic, sometimes even a 

 predominant, constituent of the secondary bast ; their occurrence however is as far 

 from being universal as is that of the fibres. They lie both in the medullary rays 

 and in the bundles, in the latter usually forming longitudinal rows with short 

 articulations ; each of these rows is derived from a single mother-cell, and may often 

 be isolated as a connected series; they were termed septate sacs at p 139 (comp. 

 Fig. 213). Guaiacum and Quillaia have already been mentioned above as forming 

 at least partial exceptions to this mode of arrangement ; it may be left an open 

 question how far similar, i. e. short, isolated sacs, may further occur elsewhere in the 

 bundles, or not ; no minute investigations on this point have been published, and 

 the statements as to the distribution of crystals, which are chiefly based on trans- 

 verse sections, do not admit of any decision on the question. The form of the 

 crystals is either klinorrhombic, or that of clusters, raphides, or granules ; one or 

 more definite forms are characteristic of each particular case (comp. p. 142, and 

 Sanio, /. c). 



With reference to the presence or absence of the crystal- containing sacs, and 

 their distribution in the former case, the following phenomena have been observed, 

 which however, at least so far as my own observations are concerned, still require 

 re-investigation. 



I indicate those forms of the crystals, which have been chiefly observed in transverse 

 sections, in parentheses (K = klinorrhombic, C = clusters, R = raphides). 



1. Crystals are absent from the secondary bast : Drimys Winter!, Fraxinus, Syringa, 

 Jasminum fruticans, INIahonia Aquifolium (?), Laurus Sassafras, Cinnamomum aromaticum 

 (Cinnamon Cassia), Clematis Vitalba, Atragene, Aristolochia Sipho (?), Camellia japonica, 

 Sorbus Aria, and, according to Hartig (Forstl. Culturpfl.), also Cornus. As regards the 

 sacs containing the crystals, the Cupressineae, Taxineae, and other Coniferae, and 

 Ephedra, are also to be included in this series, as in these the Calcium oxalate is not 

 deposited in the interior of sacs or cells, but is intercalated in the membranes. In 

 most of the plants just mentioned I find that crystals are also absent from the primary 

 cortex. 



2. Crystals are contained in the secondary bast (and then usually or always also 

 in the primary bast, and in the external cortex). In these cases they occur— 



» Berg, I.e. 36, 37. 2 Hartig, Forstl. Culturpfl. p. 13. 



Jl m 



