408 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
case of buds, but only growth by ordinary cell-division. An individual 
is a body which cannot be divided in such a way that the division gives 
rise immediately to two or more entirely new bodies. He combats the 
prevalent idea that continuous vegetative multiplication necessarily 
results in degeneration. The banana, date-palm, &c., are never repro- 
duced sexually in cultivation. Cultivated plants which are reproduced 
by seeds (cereal crops, &c.) are as liable to injury from parasitic fungi 
as those which are propagated from buds or cuttings. 
In most cases vegetative propagation has been the result of un- 
favourable conditions for the production of sexual organs or for the 
ripening of the seed. The advantages presented by sexual reproduction 
are : (1) the type of the species is more readily preserved by unispecific 
crossing; (2) by bispecific crossing the production of new species is 
(not made possible, but) rendered more easy; (3) it is a means for 
the development of more highly organised forms. There is no relation- 
ship between the complexity of the vegetative structure and that of the 
sexual organs. 
Embryogeny of Sagittaria.* — Mr. J. H. Schaflher finds the deve- 
lopment of the pollen-grain, embryo-sac, and embryo of Sagittaria 
variabilis to agree in general terms with that in Alisma Plantago. The 
generative nucleus divides into the tw r o male nuclei long before the 
dehiscence of the anther, making a trinucleated pollen-grain. The two 
polar nuclei usually fuse completely before impregnation, the centro- 
spheres and nucleoles appearing also to fuse. The three antipodal cells 
are usually surrounded by cell- walls before impregnation. The embryo- 
sac becomes divided, after impregnation, into two parts, the growth and 
curving of the embryo-sac taking place practically entirely above the 
division-wall. The pollen-tube expands, as it enters the embryo-sac, 
and passes down on one side past one of the synergids, which disappears 
at this time. The two male nuclei both enter the embryo-sac with the 
pollen-tube, but only one of them leaves the tube and takes part in fer- 
tilising the oosphere. Two very distinct centrospheres precede the male 
nucleus as it passes through the end of the tube. The apex of the tube 
appears to be ruptured by the passage of the nucleus. As the male 
nucleus approaches the oosphere, the latter developes a large bulge on the 
side facing the pollen-tube, two centrospheres sometimes appearing on 
the bulge. Centrospheres appear in resting nuclei and in division- 
stages; and, just before the contact and during the fusion of the male 
and female nuclei, two pairs of centrospheres appear, which seem to fuse 
simultaneously with the male and female nuclei. 
Cleistogamy in Umbel lifer se.f — Mr. T. Meehan describes a peculiar 
kind of cleistogamy in Cryptotsenia canadensis . It has two kinds of flower, 
male and hermaphrodite. In the latter the stamens, with short filaments 
and polliniferous anthers, are all enveloped in an extremely fugacious 
corolla, beneath which pollination is effected before the flowers open. 
Double Pollination.J — From experiments made on the hybridisation 
of several species of Marica , natives of Brazil, the late Dr. F. Miiller 
contests the assertion of Gaertner that the mixed pollination of a stigma 
* Bot. Gazette, xxiii. (1897) pp. 252-72 (7 pis.). Cf. this Journal, 1896, p. 436. 
t Proc. Acad. Nat. Sci. Philadelphia, 1897, pp. 177-8. 
t Flora, lxxxiii. (1897) pp. 474-86. 
