782 EEroiiT — 1892. 



rise to a position more or less nearly horizontal. The outer anthers are poorly 

 developed, and bear a very little pollen. A single specimen of_ the hybrid 

 (/x c) xj has just flowered, and shows some notable features, but it is not as yet 

 far enough advanced to admit of full description. 



)■ 



12. The Hmhrijo-sac of Angiosperins is a 8poroci/te and not a Macrospore. 

 By GusTAV Mann, M.B., CM. 



The development of the ovule and its embryo-sac has been studied in Myosuru't 

 minimus, L. Three stages may be distinguished : — 



1. An early stage, during which one physiological and several non-physiological 

 archespores and one physiological and two or three non-physiological embryo- sac- 

 cells are formed. 



2. An intermediary period, ending with the formation of eight sexual nuclei 

 within the sac. 



3. A final stage, during which the ovum matures and the primary endosperm- 

 cell is formed by the conjugation of two sexual primordial cells. 



A. Early Stage. — There are several archespores, but only one undergoes further 

 development, and this, the physiological one, divides into two cells, one of which 

 lies next the plerome elements of tiie ovule. This one attains a larger size, and 

 precedes in redivision its sister cell, which abuts on the dermatogen. 



Four cells are thus derived from the physiological archespore, and of these that 

 one lying next the plerome develops into tlie physiological embryo-sac ; the three 

 remaining cells must be regarded as non-physiological embryo-sacs. In all the 

 cells derived from the functional archespore, gelatiuisation of the cull-walls takes 

 place — a phenomenon quite analogous to that occurring in other sporocytes, e.(j., 

 pollen-mother-cells, and in all probability analogous to what occurs in animal ova 

 generally, the zona pellucida being the wall of a sporocyte, the ovum proper 

 equalling physiologically a female cell, the polar bodies being non-physiological 

 female cells. 



The author's view has been conflrmed by (1) Guignard, who discovered that in 

 the embryo-sac and pollen-mother cell, at the time of their formation, the number 

 of chromatin segments becomes reduced by half ; (2) by Dodel and Overton, who 

 discovered, quite independently of each other, that the synergidffi are non- 

 physiological ova, as proved by the fact that they may become fertilised and 

 develop into embryos. 



B. Intermediary Period. — The functional embryo-sac cell shows no gelatinisa- 

 tion in that cell-wall which is in contact with the plerome elements to allow n 

 ready transit of nutritive material through it. 



The embryo-sac cell enlarges, one or more vacuoles are formed, and the nucleus 

 divides. The protoplasm does not divide immediately, but does so later on, in 

 about 50 per cent, of cases, by the formation of one or two membranes separating 

 the apical half of the sac from the basal half. 



The two nuclei in the sac divide and redivide, thus giving rise to eight nuclei : 

 namely, the ovum, two synergidae, two primordial cells, and three antipodes. The 

 basal half of the sac, being supplied more abundantly with nourishment, precedes 

 the apical half in division ; its monasters are larger, &c. 



C. Final iStaqe. — As the sac enlarges the nucellar cells and the non-functional 

 embryo-sacs perish; albuminoid compounds, set free by their death, enter the 

 apical end of the physiological or functional embryo-sac, the basal end and the 

 ovum being supplied with food derived from the jilerome elements. This is the 

 reason why the nuclei of the syuergidse are placed next the dermatogen ; why the 

 nucleus of the ovum is placed next the cavity of the sac ; why the vacuoles occupy 

 respectively the reverse position. The synergidre are, normally, non-functional, 

 because want of food leads to their degeneration before the flower is ready for 

 conception. 



The two primordial cells giving rise to the primary endosperm-nucleus (Stras- 

 burger's secondary nucleus) are sexual cells ; and the resulting zygote is a true 



