ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 433 



chromatin shortly before division. The regular reticulate arrangement 

 disappears, and lumps of chromatin are formed, often with pseudopode- 

 like protuberances, connected by delicate threads of liniu. The same 

 is the case with the endosperm tissue, which subsequently fills up the 

 embryo-sac. Irregular divisions of the nucleus are very common in the 

 endosperm ; and the number of chromosomes in each nucleus is very 

 variable. In the formation of septa the kinoplastic thickening-plate in 

 the equatorial region divides, the new membrane arising in its middle. 

 Many nuclei are always enclosed in each cell, which subsequently 

 coalesce ; the combined nuclei ultimately become spherical, and are 

 distinguished from the uucombined ones by their greater size. Some of 

 the nucleoles coalesce, while others remain separate ; when quite mature 

 most of the nuclei contain only a single nucleole. In the further 

 division of the endosperm, after the coalescence of the nuclei, peculiar 

 processes take place, which may be pathological. The cells which travel 

 into the interior of the embryo-sac are at first naked, and are separated 

 by a granular protoplasm. 



The formation of the " beams " in the epiderm of the testa is 

 effected by outgrowths from the walls into the cell-cavity ; the cellulose- 

 beams are formed within them, and increase by apposition. The nucleus 

 in these cells is used up in the formation of the beams. Multinucleate 

 cells occur in the integument ; the increased number of nuclei being 

 probably connected with the thickening of the wall. 



Corydalis lutea and C. ocliroleuca agree with C. cava in the mode of 

 formation of the testa, but present considerable differences in the forma- 

 tion of the endosperm. 



Impregnation in Cucurbita Pepo.* — Prof. B. Longo describes im- 

 pregnation in the gourd as " mesogamic " {vide ante, p. 431), i.e. inter- 

 mediate between the basigamic and the ordinary acrogamic modes. The 

 pollen-tube, traversing the conducting tissue, which is here the suture 

 of the ovary, reaches the peripheral tissues of the funicle, which present 

 the same characters as the conducting tissue. When it has traversed in 

 a tortuous manner that part of the outer integument of the ovule which 

 covers the apex of the nucellus, with which the conducting tissue is in 

 connection, the pollen-tube penetrates the neck of the nucellus, either 

 by the apex or more often a little below it, and passes in a straight line 

 through the prolongation of the nucellus. Here it swells up, forming 

 a kind of bulb larger than the embryo-sac itself, which it finally reaches. 

 !No similar mode of impregnation was observed in other species of 

 Cucurbitaceae. The peculiar mode of impregnation appears to be con- 

 nected with a difference in the struct re of the ovule, and in its relation 

 to the internal wall of the ovary. 



Embryo-sac of Orchideae.f — P. Dumee has examined the embryo-sac 

 of a number of species (and genera) of Orchid ese, at a very early period 

 in its development, in order to settle the question as to its origin. At a 

 very early period the nucellus is composed of three rows of cells, all 

 resembling one another, and of nearly the same size ; later, one of the 

 cells of the axial row exceeds the rest in size, and is the mother-cell of 



* Atti. r. Accad. Lineei, x. (1901) pp. 1G8-72 (2 figs.). 



f Bull. Soc. Bot. France, xlvi. (1899) Sess. Extraord., pp xxx.-xxxii. (2 pis.). 



Aug. 21st, 1901 - ^ 



