Alexander. — On Myoporum laetum. 815 



"(a.) .... 



" {b.) In short cavities in the group ButacecB, in species of 

 Hypericum, many species of Oxalis, Myrtacece, MyoporecR." 



Also, p. 209 :— 



*' [e.) Among the Myoporea, the species of Myoporum have 

 numerous round oil-cavities of unequal size in the leaves and the 

 outer cortex of the branches. The cavities are superficial and 

 separated only by 1-2 layers of cells from the epidermis, which 

 is arched convexly outwards; e.g., M. parvifoliinn. In M. 

 tuberculatum, on the contrary, according to Unger,|they occur in 

 the middle of the chlorophyll parenchyma of the leaf. They 

 are surrounded by 1-3 layers of flattened cells. As far as 

 investigated, their origin appears to be lysigenetic." 



Observations. — I made observations on the leaf and stem of 

 M. latum through the autumn and winter, examining sections 

 through fresh specimens and specimens preserved in alcohol, 

 with the following results : — 



In a piece of mature leaf, 2*5 ths of a square inch, there were 

 164 glands. This gives 1,025 to the square inch, so that about 

 1,000 to the square inch appears to be a fair average of their 

 number. They are, however, much fewer towards the base of 

 the leaf, near the insertion of the petiole on the stem, but are 

 not altogether absent. In the lamma they occur both in the 

 parenchymatous tissue and also in the midrib (see fig. 4), and 

 are entirely surrounded by two or three layers of compressed 

 colourless cells (see figs. 1 and 2). 



The upper epidermis is often arched outwards over the 

 glands (see fig. 1), but there are always at least two rows of 

 cells between the epidermis and the compressed cells surrounding 

 the gland, one of the rows being palisade cells. The cells of 

 the palisade parenchyma above the gland are also colourless. 



The glands vary in size from ^V~tV ^^^*^^ ^^ diameter in 

 the lamina ; in the midrib and stem they vary even more, some 

 being found considerably smaller. The shape of the gland is 

 spherical, and in the dried specimen which I examined the con- 

 tents had aU fallen away from the centre, forming a granular 

 colourless coating round the inside of the gland, enclosing a 

 vacuole. In the specimens preserved in alcohol, the contents 

 had coagulated into little brownish-yellow masses, apparently of 

 gum. (See fig. 2.) 



In very young leaves there are no glands (see fig. 5), but 

 they begin to appear when 10 or 12 leaves are formed nearer 

 the apex (fig. 6). The rapid growth of the young leaves appears 

 to retard the formation of the glands, but after their first appear- 

 ance they are soon found in considerable numbers (fig. 6). 



In the stem the glands appear both in the pith and cortical 

 parenchyma (fig. 7). Their occurrence in the pith is not men- 

 tioned by Hooker or De Bary. They are scattered irregularly 



