454 MR. J. R. GREEN ON THE ORGANS OF 
distributed. It takes the form of narrow passages, observable 
only in the young phloém of certain species. 
The mode of origin of the cavities of the oil-reservoirs has 
been for a long time a matter of controversy. Two views have 
been maintained, and both have had many advocates. According 
to some they are merely a modification or extension of inter- 
cellular spaces; while others hold them to arise from absorption 
of masses of cells. That they are of schizogenous nature was 
first advanced by Kieser*, who, writing in 1812, says that they 
are intercellular passages and arise from intercellular spaces. 
Meyen, in his work ‘ Ueber die Secretionsorgane der Pflanzen,’ 
published at Berlin in 1837, takes the same view, which has also 
been advocated by Von Mohl. In later years this mode of origin 
has been ascribed to them by Frank f. Writing in 1868 upon 
the glands of Myrtus and Hypericum, he describes his method of 
investigation. In the former genus, to which he paid most 
attention, he cut sections parallel to the surface of the leaf and 
mounted them in glycerine. He says that the glands originate as 
a single rather large cell, having granular contents. This cell 
divides by three walls at right angles to each other, forming 
eight cells, which separate from each other at their common 
apex. Into the space so formed the secretion is poured, and 
thence it makes its way towards the periphery of the gland, 
forcing the cells apart. Coincident growth made the cells flatter, 
so that the gland became a spherical cavity, lined by the cells. 
The number of these increases by division of one or more of 
them. Having thus described the origin of the glands in Myrtus, 
he argues the same mode of formation for those in Hypericum 
perforatum, from the analogy of the clear spaces in that plant with 
those in Myrtus. Investigation into his method of working at 
Hypericum, however, shows that there was room for much error 
to enter into his conclusions. .He did not examine sections, as he 
says he could not cut them parallel to the surface, the leaves 
being too thin. He mounted young leaves in glycerine, when, he 
says, the epidermis was transparent enough to let him see the 
stages in the formation of the gland. He has figured what he 
took to be the condition of the octants at the moment of their 
separation from each other. ; 
In 1882 a paper was contributed to the S.B. k.-k. Akad. Wiss. 
* ‘Mémoires sur l'organisation des Plantes’ (Haarlem, 1812), p. 107. 
t ‘Beiträge zur Pflanzenphysiologie, p. 124 e£ seg. 
