ZOOLOGY AXD BOTANY, MICROSCOPY, ETC. 567 



small portions. The parenchyma sheath is usually conspicuous and 

 large-celled ; in Phlox amocna and P. Drummondii it takes the form of an 

 endodermis, its numerous cells having cuticularised radial and tangential 

 walls, while in Gilia pungens its cells are woody, with U-shaped 

 thickenings. 



Usually the pollen is spherical ; it is ellipsoidal in most species of 

 Collomia and a few of Gilia, and polyhedral in Gollomia aristella. It is 

 honeycombed in Gobcea, Phlox, some species of Gollomia and Gilia and 

 a few others ; smooth in Gilia latifolia ; has wavy ribbing in species of 

 Collomia and Gilia ; meridional ribs in Gollomia grandifiora, Gilia sp., 

 and the Polemoniums except P. mexicanum ; and is warted in Bon- 

 plaiidia, Cantua, and Loeselia. 



The testa is three-layered — (1) epidermis, (2) compressed layers, 

 (3) pigment layer — in many cases. In Gobma it is of four layers, lignified 

 cells being interposed between (1) and (2), while in Loeselia ^\\(\. Gilia sp. 

 the lignified cells are replaced by mechanical tissue. The testa of Phlox 

 has only layers (1) and (2). In all genera except Phlox the epidermis 

 cells swell up when moistened ; they are thickened in most cases with 

 spiral bands or rings. The slimy matter lies outside the spiral in Bon- 

 plandia, Gantua, Goimi, Collomia, and a few more ; in the rest it lies 

 within the spiral thickening. 



Ruellia and Dianthera : an Anatomical Study.* — T. Holm has 

 studied two species of Acanthaceae very common near Washington, 

 Ruellia ciliosa Pursh. and Dianthera americana L. The former has the 

 monostelic stem-structure characteristic of most Dicotyledons ; in the 

 latter the interesting discovery is announced of its possession of a 

 polystelic axis. Ruellia ciliosa has root-shoots belonging to Wittrock's 

 second or " additional " type. These have a cortex of three zones ; a 

 peripheral zone of thickened cells with cystoHths ; a middle or thin-walled 

 cell with some thick-walled sclerotic cells and cystoliths, but without 

 raphids and starch ; and a typical endodermis. Within is the pericambium 

 which surrounds the mestome with its stereome, the latter presenting 

 itself as four strands outside the leptome. In the latter raphidines are 

 very rare, and never more than one in a cell. The above-ground stem 

 has collenchyma surrounding a cortex with cystoliths and raphids, but 

 no sclerotic cells and no starch. The mestome strands are collateral, and 

 there are a few cambium-layers between leptome and hadrome, but none 

 outside the medullary rays. The pith has raphids and crystals of various 

 forms, but neither starch nor cystoliths. In the leaf the mechanical 

 tissue is present only in the form of hypodermal strands of thick-walled 

 collenchyma, there being no stereome. Water-storage tissue occupies 

 the greater part of the midrib above and below the mestome bundles ; 

 these are all collateral, those forming the midrib being arranged in a 

 broad arch, concave upwards ; the leptome consists of several groups 

 under the hadrome, and also occurs as small isolated strands between the 

 hydromic rays. Endodermis is present on the leptome side only ; it 

 forms an open arch, like that found by Roulet in species of Thunhergia. 



* Bot. Gazette, xliii. (1907) pp. 308-28 (2 pis.). 



