642 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
developed ; the leaves are thicker ; the cells of the palisade-tissue more 
elongated, and the air-chambers larger. 
Male Organs of Gymnosperms.* — M. Thibaut calls attention to the 
difference in structure between the male organs of the Coniferae and 
Cycadeae on the one hand and those of the Gnetaceae on the other hand. 
In the Cycadeae the stamen consists of a scale which bears the pollen- 
sacs on its under side. The scale or vegetative portion of the stamen is 
large and well developed. It consists of one or two much-branched 
vascular bundles, an epiderm with a strongly developed cuticle, and a 
dense layer of fibres and sclerites, deposits of tannin and calcium oxalate, 
and secretion-canals. The pollen-sacs have a septum formed either of 
a single layer of epidermal cells or of a layer of hypodermal fibres. 
The epiderm, which represents the elastic zone of the septum, is dis- 
tinguished from the epiderm of the rest of the stamen only by a stronger 
development of its cutieular layers and by the lignification of its lower 
region. Its cell-walls are strongly thickened on their lateral sides. 
The same type occurs, with more or less variation, in all Conifers, the 
variations depending mainly on the degree of reduction of the scale and 
on the diminution in size of the pollen-sacs. In the Araucarieae, Taxo- 
dieae, and Cupressineae, the pollen-sacs are obviously on the lower [upper 
in Bot. Centr.] side of the scale, in other Coniferae they exhibit a tendency 
to become depressed. As the vegetative portion of the stamen becomes 
reduced in size, it exhibits also a simplification in structure, while that 
of the pollen-sac becomes more and more complicated. 
The Gnetaceae, in contrast to the Cycadeae and Coniferae, possess 
perfect male flowers. The pollen-sacs are not placed on one side of a 
scale, but on the apex of so-called supports (staminophores). They 
open by a fissure at their apex. The epidermal cells have no thickening 
zone, but, on the other hand, curved septa ; those of all the other Gymno- 
sperms being flat. 
Sporophyll of Cycadeae. f — Mr. W. C. Worsdell has studied the 
vascular structure of the sporophyll in a number of species belonging 
to different genera of Cycadeae. He finds, in the male sporophyll, a 
single vascular bundle leaving the cylinder of the axis of the cone, 
which, on entering the stalk of the sporophyll, divides into three. The 
bundles supplying tho sporanges are much smaller in size than the 
similar ones on the female side. They also diverge less from the mesarch 
structure of those of the foliage leaf than do the bundles of the female 
sporophyll. In the female sporophyll two bundles leave the cylinder 
of the axis of the cone, usually dividing up in the cortex into a larger 
number, so that, as a rule, four bundles occur in the stalk of the sporo- 
phyll, of which the two lateral ones are much larger than the rest. The 
divergence^ from the ordinary mesarch structure of the foliage leaf is 
here much more marked. In the sterile portion of both kinds of sporo- 
phyll, i.e. in the part above the insertion of the sporanges, the mesarch 
structure of the bundle prevails. As compared with the bundles of the 
stalk, the centripetal is, as a rule, much more developed than the centri- 
* ‘ Rech. s. l’appareil male d. Gym nospermes,’ 225 pp. and 1G pis., Lille, 189G. 
See Bot. Centralbl., lxxv. (1898) p. 129. 
t Ann. of Bot., xii. (1898) pp. 203-41 (2 pis.). 
