20 Shirley and Lambert : 



gave a general review of these curious leaf organs, dealing especi- 

 ally with the histology of the leaf of Pennantia Cunninghamiiy 

 Miers, and figuring a hair from the pit of Coprosma lucida, Forst. 

 Both of these writers (6, 7) lay much stress on the use of the pits, 

 as a habitation for Acarina, though Hamilton acknowledges that as- 

 often as not the pits were found without guests. Where mites were: 

 numerous he found the walls of the cavities damaged, showing brown- 

 ish patches and bright crimson cells. It is remarkable that the 

 kaikomako or New Zealand Pennantia is in its young state a shrub, 

 whose flexuous interlacing branches and small distant sessile leaves 

 give it the aspect of a xerophyte; while in its mature stage it is a 

 tree, 20 to 30 feet high, with stalked glossy leaves two inches in 

 length. A very important paper on the Coprosma leaf pits is that by 

 Miss N. A. R. Greensill(8), dealing with the minute structure of the 

 leaves of ten New Zealand species, and reviewing all work on the 

 subject to date. Miss Greensill utterly failed to find insect guests- 

 in the so-called domatia, either in species cultivated in gardens and 

 public parks, or in those growing under natural conditions; she found 

 some pits in an unhealthy state with brown patches and crimson- 

 coloured cells, but traced these changes to attacks of fungi. Miss 

 Greensill favours the view that the pits absorb moisture. Mr. Nathan 

 Banks (9) figures three structures in leaves caused by Acarina, which 

 he terms dimple gall, capsule gall, and pouch gall respectively, caused 

 by mites Eriophyes pyri. The pear-leaf blister mite is found in Aus- 

 tralia. 



3. Histology. 



J. Leaf Structure of C. Bauerl. 



The pits lie on each side of the midvein, at junctions with 

 primary veins, and vary in number from fo-ur to nine; those in the 

 lower part of the leaf are often immature and closed, when the upper 

 ones are mature and open. Very rarely are they found on the prim- 

 ary veins; and in each case noted this abnormal position was limited 

 to a single pit. In transverse section, fig. 1), the leaf shows an. 

 upper epidermis of three layers. The first is constructed of small 

 ovate cells, with their longitudinal axis parallel to the surface, ir- 

 regular in size, the longest about 31^/. This layer is clothed ex- 

 ternally by cutin measuring one-half to one-third the transverse 

 diameter of a cell. The units of the second layer show no cell con- 

 tents, and are polygonal in outline; their greatest diameter is 65^. 

 The third layer is composed of cells (fig. 2) showing transition 

 forms between those of the second layer and palisade cells, the; 

 shape is rhomboidal or rhombo-polygonal, and the long axis is at 

 right angles to the surface, the greatest length is 33^^. Palisade cells 

 proper are in three rows, slender in outline, 54 long, three or four 

 abutting on each pair of third rank epidermal cells. The spongjr 

 parenchyma (fig. 1), shows cells of various outlines — oval, globu- 

 lar, dumb-bell shaped, etc., seldom exceeding 35,, in diameter. The- 

 interrcllular spaces between them are very small; with the excep- 

 tion of those near a pit they communicate by numerous small stomata. 



