294 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Primula , the usual structure of the cauline bundles is reversed, the xylem 
facing the periphery, the phloem the centre of the column. But, 
according to M. E. Decrock, this is not invariable in all species of the 
genus. It is the case in P. sinensis and viscosa ; but in P. acaulis, verti- 
cillata, stricta , elatior , and officinalis , the phloem of each vascular bundle 
completely surrounds the xylem, the xylem vessels first differentiated 
occupying the centre. In P. scotica , longtflora, and marginata, the bundles 
are also concentric. 
Structure of the Alstrcemeriese.* — Dr. A. Colozza has studied the 
morphology and anatomy of this natural order, especially in regard to 
the relationship to Alstroemeria of the genus Bomarea , which agrees with 
the typical genus in some points, while differing from it in others. In 
both genera there is developed a mechanical ring in the aerial stem and 
in the rhizome below the cortical parenchyme. While in Alstroemeria the 
vascular bundles display a tendency to arrange themselves in two circles, 
in the species of Bomarea studied by the author the vascular bundles 
are regularly arranged in three circles. 
Structure of Lemna minor. f — Mr. O. W. Caldwell has made a care- 
ful study of the life-history of the common duck-weed. The following 
are among the more important results. 
There is no true differentiation of stem and leaf. The secondary 
root is formed from a group of hypodermal cells. The epiderm persists 
for a considerable time as the temporary root-sheath. The root-cap 
adheres while young to the main body of the root, but becomes entirely 
free later except at the growing point. Flowers are rarely formed ; 
fertile seeds still more rarely. A single archesporial cell occurs in each 
stamen ; this divides later into 2, and then into 4 masses, each constitu- 
ting the archesporial mass of a loculus. The primary tapetal layer is 
not cut off at the first division of the archesporial cells, but after these 
have become separated into 4 regions. The microspores (pollen-grains) 
germinate within the sporange. The generative cell remains closely 
applied to the wall of the spore for a time before dividing. In the 
megasporange (embryo-sac) the primary tapetal cell usually undergoes 
no further division, while the primary sporogenous cell passes directly 
into the megaspore. Normal embryo-sac structures are rarely developed. 
(4) Structure of Organs. 
Replacement of one Organ by another.^ — M. A. Boirivant gives 
the following general results of experiments on this subject. 
The removal of the leaves (or the blades) causes a larger develop- 
ment of chlorophyll, and consequently a deeper colour, in the stem and 
petiole, and a modification in the structure of their tissues, with an 
increase in the number of stomates ; and, in consequence, an increase in 
the power of assimilation and of transpiration, of those organs. 
When a primary root is removed, the radicle which takes its place 
partakes more of the character of a primary than of a secondary root. 
The same is the case with secondary branches which take the place of a 
primary branch. 
* Malpighia, xii. (1898) pp. 165-98 (2 pis.). 
t Bot. Gazette, xxvii. (1899) pp. 37-66 (59 figs.). 
% Ann. Sci. Nat. (Bot.), vi. (1898) pp. 309-400 (5 pis.). 
