552 



SECONDARY CHANGES. 



The position of the latter, as is probable a prion from the occurrence of 

 transitional forms, is not determinate in a sense generally applicable to all cases. 

 It lies : — 



(a) At a relatively great distance from the bast-layer ; this is conspicuous in 

 the case of Berberis vulgaris, where it borders immediately on the broad sclerenchy- 

 matous ring of the external cortex (p. 419), and is separated from the phloem- 

 bundles by a broad zone of lacunar parenchyma containing chlorophyll. The same 

 is the case in shrubby Papilionaceae like Sarothamnus, Colutea, and Coronilla 

 Emerus ; also in Ginkgo ; Caragana arborescens ^ and the stems of perennial 

 Caryophyllacex (Dianthus, Silene spec.) have the cork-layer close inside the 

 sclerenchymatous ring, which is separated from the bast by a zone of parenchyma. 



The formation of periderm in Casuarina 

 and the Abietineae, which, on account of 

 some peculiarities, must be more minutely 

 considered below, may also be placed in 

 this category. 



((5) It lies near the external limit of the 

 bast-layer, and in fact, in the absence of 

 distinct fibrous bundles at the outer boundary 

 of the phloem-region, in immediate contact 

 with the latter : Lycium barbarum, Cobsea, 

 Ribes (Fig. 220), Deutzia scabra, species of 

 Lonicera, many Melastomace^ (JMelastoma 

 Heteromallum, species of Lasiandra and 

 Heterocentron -), Thuja, and Juniperus ; 

 Atragene and Clematis may also be men- 

 tioned here rather than in the category with 

 bundles of bast-fibres. Where the latter are 

 present, the phellogen either lies immediately 

 outside them (Rubus idseus, according to 

 Sanio), or close to their inner boundary 

 (Punica, Spirsea opulifolia, Philadelphus, 

 Melaleuca, and Vitis). In the INIelasto- 

 macese mentioned, the initial layer borders 

 directly on the endodermis which surrounds 

 the bast. How far such a relation to a 

 plerome-sheath occurs elsewhere, remains to be investigated. 



The succession of the divisions is, in the cases belonging to this series in- 

 vestigated by Sanio, centrifugally reciprocal (Berberis, Caragana, Lycium, Deutzia, 

 Lonicera, Philadelphus, Rubus, and Melaleuca) ; in the Melastomese and Casuarina 

 it is centripetal. In the other cases mentioned the order of division has not been 

 more minutely investigated. 



Phelloderm is formed in Ribes, Lycium, Caragana, Deutzia, Lonicera, and 

 Spiraea, and also, as it seems to me, in the Cupressineai mentioned; in the re- 



FIG. 2-.>o. — Transverse section through the surface of the 

 cortex of a or.e-year-old branch of Ribes nigrum (500). e 

 epidermis, A hair, /rdried-up and distorted parenchyma of 

 the external cortex, i external region of the bast; A' peri- 

 derm, consisting of the suberous integument i, phelloderm 

 containing chlorophyll /fl', and the phellogenetic layer of 

 meristem at c. From Sachs, Textbook, 



* Sanio, Stahl, /. c. 



^ Vochting, /. c. p. 5 1 . 



