134 ANATOMY AND PHYSIOLOGY OF 



being preserved for a year in the East ; and the name time ha^ been 

 asserted for Cannabis, Zea, and Cmmllia. (See Gartner " BefrucMung der 

 Gewachbe,'' 1, 146.) 



In order to explain the course of the processes which go on in 

 the interior of the ovule, it will be necessary for me to return to 

 its structure. Towards the epoch of impregnation, the embryo- 

 sac has mostly become greatly enlarged in proportion to the other 

 parts. In many plants it is still enclosed in the interior of the 

 nucleus, so that its upper end, directed towards the micropyle, is 

 still covered by one or more layers of parenchymatous cells be- 

 longing to the nucleus. In other plants (for example in the Or- 

 chidese and Syngene&ia), the embryo-sac (pi. 1, fig. 12, s; 13, s) has 

 by this time wlioUy displaced the entire nucleus, or at least the 

 upper part of it (in the Leguminosse also the inner coat of the 

 ovule), and in certain cases, in particular in Santalum, has be- 

 come so much elongated that it projects freely out of the micro- 

 pyle. The pollen-tube which has penetrated into the micropyle 

 (pi. 1, fig. 14, _p : 1 5, 2>.) in its further elongation, thus comes either 

 immediately in contact with the apex of the embryo-sac, or with the 

 layer of cells coveiing it ; in the latter case it penetrates between 

 these cells, and in this way likewise reaches the embryo-sac. 



In the latter there is always a more or less abundant quantity 

 of protoplasm. In the later period, just before the pollen-tube 

 reaches the embryo-sac, a portion of the protoplasm becomes at- 

 tracted into the upper end, next the micropyle. In this proto- 

 * plasm nuclei appear, usually to the number of three (pi. 1, fig. 12), 

 and give lise to the formation of as many cells (pi 1, fig. 13, b; 14), 

 which more or less completely fill up the npper part of the cavity 

 of the embryo-sac, and are termed the germinal vesicles {embryo- 

 blaschen). The triple number, although usual, is not universal, 

 for in many plants (e. g., Agrostemma Gfithago, according to Hof- 

 meister) only one germinal vesicle is formed, while in other cases, 

 as in Funckia coerulea, a larger number present themselves. One 

 of them also, as Hofmeister observed in Ganna, may displace the 

 rest before impregnation through its predominating enlargement. 

 "With these cells necessary for the origin of the embryo, a variable 

 number of other cells are also formed in other parts of the embryo- 

 sac (pi. 1, fig. 4, /), chiefly in the end turned away fi:om the mi- 

 cropyle, more rarely in the central region. But this cell-formation 

 is neither an universal phenomenon, nor does it stand m relation 

 to the impregnation. 



When the pollen-tube has reached the upper part of the embryo- 

 sac, its growth is either immediately arrested, or it becomes elon- 

 gated a very little more, so that its obtuse, somewhat inflated end 

 usually penetrates laterally between the embryo-sac and the sur- 

 rounding cellular layer (pi. 1, fig. 14^ 15), or, in rare cases (Ifareis- 

 sus poeticus, according to Hofineister ; Digitalis purpurea, and 

 Campanula Medium, according to Tulasne), introverts the mem- 



