10 



Transactions. 



strongly 



margins 



Longitudinal sections of old. stems show as follows : Pith of rectangular 

 cells lignified, fairly regular, from two to three times as long as broad. 

 Xylem mainly of fusiform tracheides with walls strongly lignified and 

 pitted. A few large cylindrical pitted vessels or tracheae occur, the original 

 transverse walls showing at intervals as an internal ring. Cambium : Single 

 layer, thin-walled. Phloem composed mainly of elongated cylindrical cells 

 and a few sieve-tubes. External to the phloem comes a rather confused mass 

 of tissue, but in most cases in old stems the cortex has been shed, and the 

 endodermis surrounded by one, or at the most two, layers of flattened cork 

 forms the outer covering. 



(b.) Leaf. — The leaf of this species is polymorphic. In old plants, what 

 may be considered as the typical form is oblong-lanceolate or linear-lanceolate. 

 The leaves have the margins on the lower half parallel, and a little past half- 

 way they gradually taper to an acute apex, 

 which has a distinct blunt papillose point of 

 a pale-yellow colour. The blade is slightly 

 folded inwards, and the tips are reflexed. 



Typical leaves are very slightly hairy 

 with long white silky hairs on both surfaces. 

 Length of leaf, 3-4 mm. 



In many cases the leaves are 

 conduplicated. so much so that the 

 of the distal half of the blade meet towards 

 the tip, and give a general subulate form to 

 the whole leaf. The ph} T llotaxy is spiral. 



This pseudo - subulate form may be re- 

 garded as the typical adult condition of the 

 leaf, but younger ones do not exhibit this 

 ■ — they may be thus described : Broadly 

 spathulate, tip almost truncate, minutely 

 apiculate ; whole leaf much recurved ; margins 

 incurved ; narrowed to a broad sheathing 

 base ; total length, 6 mm. ; broadest part. 

 2-5 mm. Whole leaf rather densely covered 

 with a felt of silvery hairs lying more or 

 less parallel to midrib, closely appressed to 

 epidermis. Midrib and veins indistinct. This 

 is the type of leaf found on seedlings and 

 on terminal branches of young shoots (fig. 2). 

 The hairs, which are very long, arise from an epidermal cell which gives 

 off a short branch near its junction with another cell at its distal end. On 

 this branch or basal portion of hair the long, tapering, more or less twisted 

 hair-cell is formed, separated by a septum from the basal portion. The 

 hair-cell is not septate ; it is not easily wetted. The epidermal cells are 

 polygonal, and their lateral walls are not wavy, but smooth. 



The rosettes are from 3 mm. to 4 mm. across. About six leaves are 

 visible from above in each rosette. Owing to the leaves being linear, and 

 their not being closely appressed to the axis of the branchlet, leaves of 

 adjacent rosettes interlock somewhat, so that the surface of the mat is not 

 marked out into very distinct rosette-areas. 



A transverse section of a young leaf is as follows (fig. 3) : Epidermis 

 same on both surfaces ; weak cuticle ; cells barrel-shaped in transverse 

 section. Stomata on both surfaces ; normal. Air-cavities (substomatal) 



Fig. 2. — Raoulia tenuicaulis. 

 Young shoot from a shaded 

 mat. (Hairs not shown.) 



