ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
69 
isolated patches of cambium appeared in the outer cortex and caused 
still further breaking up of the endodermis. Ultimately the rudiments 
of two secondary bundles appeared in the cortex, and subsequent 
sections showed a rapid development of secondary tissue all round the 
root from both internal and external cambium ; the endodermis. was 
now almost completely broken up into patches of isolated cells. In a 
second root of a more woody nature the secondary cambium first appeared 
in the outer cortex and gave rise to several isolated bundles ; secondary 
cambium was then formed in different parts of the pericycle, and, 
extending outwards, broke through the endodermis to meet the outer 
secondary cambium. Ultimately the two sets of cambium united and 
formed a typical continuous cambium, giving rise to secondary bundles 
and conjunctive tissue. The interruption of the endodermis appears to 
be “an adaptation to allow of a greater increase in girth of the root for 
the formation of new vascular tissues, and for a quicker interchange 
between the outer and inner tissues of the enlarging root. S. G-. 
Vessels in Seed-plants. — M. 0. Bliss (Bot. Gaz ., 1921, 71, 
314-26, 5 pis.). M. C. Bliss has investigated the origin of the vessel 
in Pteris, in the Gnetales and in the Dicotyledons, and finds that 
while in Pteris the primitive vessel is scalariform, in the Gnetales it is 
pitted. In Pteris the scalariform perforation of the end wall often 
becomes pitted, but in Gnetum scandens the more or less regular fusion 
of pits results in a scalariform perforation. In the typical Gnetum 
vessel, however, haphazard fusion of the pits gives rise to a porous 
perforation. Similar haphazard fusion of pits occurs in Pseonia, Gydonia 
and Leea , while in Liriodendron , Magnolia , Betula , Alnus, Quercus, Vitis 
and some species of Pseonia, the fusion may be serial and result in 
scalariform perforations. The evolution of the perforations of the 
vessels in the Gnetales and Dicotyledons appears to be similar, resulting 
in both cases from pit-fusions. Examination of primitive parts of 
Liriodendron , Magnolia , Pseonia and Vitis shows that the primitive vessel 
of Angiosperms is pitted and has been derived from the pitted tracheid. 
• S. G. 
Reproductive. 
Pollination of Incarvillea. — E. M. Cutting {Ann. Bot., 1921, 35, 
63-71, 3 figs.). Incarvillea Belavayi has a large sensitive stigma, and 
anthers with stiff prongs for opening the anther-lobes and setting free 
the pollen. Each anther has two such prongs, which are so arranged 
that one lobe must open and liberate its contents when the insect 
enters the flower, and the other lobe when the insect passes out. 
The pollen-grains resemble those of Thunbergia alata as described 
by Goebel, but differ slightly in the slits of the exine ; in the latter 
species these slits form one or two continuous lines, but in Incarvillea 
they only join occasionally. The pollen -grains are dry, and are able to 
germinate in quite low temperatures in the open air, but fail to do so 
under artificial conditions, even at high temperatures. The closing of 
the slits when the grains are dry and the high osmotic pressure of their 
contents may be regarded as adaptations to prevent excessive loss of 
water during transmission of the pollen. S. G. 
