42 
PROGRESS OF MICROSCOPICAL SCIENCE. 
impurities entangled in the paste are unequally distributed, and form 
more or less coloured zones analogous to those exhibited by matters 
suspended in a moving liquid. In this amorphous paste fibrous 
globules, like those of total extinction, are frequently observed, but 
the optical properties resulting from the radiated structure are domi- 
nant, and, instead of becoming extinct at a definite position of the 
prisms, these spheroliths exhibit in all positions a black cross in the 
direction of the principal planes of the- prisms. At the close of the 
series of Permian porphyries the paste becomes entirely vitreous, and 
often presents the retreating cracks, roughly concentric, which charac- 
terize the perlitic texture. In the midst of this perlite paste the 
radiating spheroliths are often well developed, and a great part of 
the pyromerides ought to be grouped with the pitchstones. The acid 
rocks of the recent period present under the microscope a striking 
analogy with ,the ancient ones, but may be distinguished by the 
nature of their included crystals. 
The Pollen of the Cherry. — Mr. A. W. Bennett writes a letter to 
* Nature' of May 11 in explanation of the form of the pollen which 
he there figures. He states that he is compelled to do this from the 
fact that it is imperfectly drawn in the figures in Balfour's, Le 
Maout's, and Dr. Hooker's (primer) works. He states that " though 
somewhat variable in size and form, the grains are, I believe, never 
spherical, but ellipsoidal, with three longitudinal furrows." 
The Circulation of the Sap. — In ' Flora,' * a German botanical 
journal of considerable interest, there is a review of Mr. Clark's 
lecture on the circulation of the sap in plants. An American journal, 
criticising it, says " the reviewer is discriminating, and points out 
some possible errors of interpretation, but appears to have thoroughly 
appreciated the wide range of experiments, and the energy with which 
the work was done." 
Structure of the Leaves in Grasses. — In the ' Annales des Sciences 
Naturelles ' I ajjpears an elaborate article on this subject by M. J. 
Duval- J ouve. Criticising this, Professor Asa Gray says : — " Many of 
the text-books still say of the leaves of grasses, and indeed of Mono- 
cotyledons generally, that their veins or nerves are simple and uncon- 
nected by anastomosis ; although what was meant must have been 
that the only anastomosis was by ultimate transverse veinlets. Duval- 
J ouve cites a long list of grasses in which these are conspicuous ; and 
there are many in which the reticulating veinlets are of diflerent 
orders. The stomata of grasses are in some confined to the lower 
surface of the leaf ; in others divided between the two faces ; in several 
they are restricted to the upper face, but in these the blade makes a 
turn or twist, so as for the most part to present this upper surface to 
the ground. Triticum junceum, Calamrogastis (Psamma) arenaria, and 
Gynerium argenteum (Pampas grass) are cited as instances. Many 
grasses have under the epidermis of their upper face, and sometimes 
of the lower also, rows or bands of large thin-walled cells, which our 
author names hulliform cells. These in their presence, absence, 
* No. 29, 1875. t Tome i. series 6. 
