1S92.] NEW-YORK MICROSCOPICAL SOCIETY. 83 



the walls remaining exceedingly delicate and transparent. Crys- 

 tals appear in this delicate cellulose sack, embedded in a gelatin- 

 ous medium which completely fills the chamber. About the 

 crystal is a film which on treatment with iodine shows the re- 

 action of cellulose (Fig. 15). The crystals belong to the mono- 

 clinic system, though the corners are often blunted and irregular 

 forms result (Fig. 16). Crystals also appear irregularly scat- 

 tered through the parenchyma. With the sclerenchyma alternates 

 the soft bast, wS. With the pressure of growth these cells are 

 much distorted, and the delicate sieve tubes are so much com- 

 pressed as to lose all trace of structure and perhaps entirely dis- 

 appear. These tubes, in the cases where examination is possible, 

 appear in the parenchyma adjoining the liber fibres, and thus 

 corrsspond to the annual zones. Their lateral walls seem to be 

 destitute of plates and the cribrose septa are nearly horizontal. 

 They greatly exceed the parenchyma in length, but have about 

 the same transverse measurements. These bundles of paren- 

 chyma and sclerenchyma correspond closely and, I believe, 

 exactly with the annual zones of the wood ; the outer ones being 

 compact, with an excess of fibre, while the inner bundles of the 

 phloem are generally characterized by an absence of fibre and 

 the soft bast is multiplied to several layers, giving a loose struc- 

 ture. This development presents a striking parallel to the dense 

 heart growth of the xylem and its later light structure. A 

 marked characteristic of the phloem is the presence of resin 

 receptacles. These are arranged in concentric circles follow- 

 ing the parenchyma in its growth, but never appearing in the 

 medullary ray. As viewed in cross-section they occupy from one 

 to several cells and give a banded structure to the bast. The 

 resin has the appearance of gamboge. It is an exceedingly inert 

 mass, little affected by strong acids, and slowly dissolves in 



ExplHiialion of Plate 34. 



Fig. 5. Cross-section of stem. E, cork ; K, parenchyma of periblem ; C, cortical 

 sheath ; R, resin sack ; B, bast fibre ; F, crystal fibre; S, parenchyma of the bast ; M, 

 cambium tissue ; T, a portion of three tracheids, showing at X an absorbed septum ; V, 

 trachea with tyloses, and a portion of its pitted wall ; P and I, forms of wood paren- 

 chyma ; L, liber fibre. X 500.— Fig. 6. Cross-section of stem lettered as in Fig. 5. D, 

 medullary ray. x .300.— Fig. 7. Tangential section lettered as in Fig. 5, showing a 

 layer of much thickened cork cells with pits. X 500.— Figs. D and E Radial and cross- 

 sections of medullary ray, showing pitted walls. X 500. 



