358 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
morphological characters in the classification of plants, in relation to 
the following organs — (1) The organs of reproduction : — pollen, 
stigmatic papillaB, integument of the ovule and seed, endosperm and 
embryo; (2) The vegetative organs: — size of the cells, epiderm, hairs, 
stomates, crystals of calcium oxalate, laticiferous and other internal 
secreting organs, structure and arrangement of the vascular bundles, 
palisade and spongy parenchyme, sclereids, mechanical system, &c. 
B. Physiology. 
(1) Reproduction and Germination. 
Morphological Phenomena of Fertilization.* — M. L. Guignard sums 
up the conclusions of previous observers on the morphological jdienomena 
on which depends the impregnation of the oosphere in flowering plants. 
His observations were made chiefly on Lilium Martagon, with which are 
compared the phenomena in Fritillaria, Tulipa, Muscaria, AgrapMs, Iris, 
Alstroemeria, Aconitum, Delphinium, Clematis, and Viola, and the results 
obtained by Van Bene den | with Ascaris megalocephala. 
His general conclusions are in harmony with those of Strasburger 
rather than with those of Van Beneden, viz. that an actual coales- 
cence of the male and female elements, and not merely their coexistence 
in the oosphere, is necessary to impregnation ; a fusion of the nuclear 
cavities being apparently essential. In the fusion of the two polar 
nuclei to form the secondary vegetative nucleus of the embryo-sac, these 
two nuclei may remain distinguishable from one another, and invested 
each by its own delicate membrane, until the period of the commence- 
ment of cell-division, which may not take place until some days after the 
entrance of the pollen-tube into the embryo-sac. He finds the number 
of chromatic segments to be the same in the male and female nuclei, and 
the double number,, viz. 24, is always to be detected after impregnation. 
In the process of division of the nuclei of the endosperm, resulting from 
the repeated division of the secondary nucleus of the embryo-sac, the 
number of chromatic segments varies considerably. 
When the original nucleus of the pollen-grain divides to produce the 
vegetative and reproductive nucleus of the pollen-tube, and when the 
reproductive nucleus again subsequently divides into two, the number of 
chromatic segments in the two is again the same, but the cytoplasm is 
distributed unequally in these two new cells, and its microchemical 
reactions are not alike. The formation of the generative nuclei, compar- 
able to that of the pronuclei in animals, always takes place by the 
longitudinal doubling of the chromatic segments. The preliminary 
phenomena which take place within the embryo-sac differ in a remarkable 
point from those which take place within the pollen-grain. In Lilium 
and probably in other plants also, the two tetrads which result from the 
bipartition of the primary nucleus of the embryo-sac, and which occupy 
the two extremities of the sac, present an imj)ortant difference, which is 
transmitted to their derivatives. Each of the nuclei of the apical tetrad 
has always twelve chromatic segments, like the primary nucleus, while 
each of the nuclei of the basal tetrad lias a larger and variable number. 
* Bull. Soc. Bot. France, xxxvi. (1889), Actes du Congres de Bot., pp. c.-cxlvi. 
(4 pis.), and Comptes Rendus, cx. (1890) pp. 590-2. 
t Cf. this Journal, 1888, p. 428. 
