354 BOTANICAL GAZETTE [November 



opening, and later stages were collected from time to time until the 

 seeds were almost mature. 



MEGASPOUE 



As is well known, the ovary of orchids contains a great number of 

 small ovules arranged in three double rows. The ovules are very 

 slow in developing, but the archesporial cell is differentiated in the 

 bud. No parietal cell is cut oiT, the archesporium functioning as 

 the spore mother cell. The young ovule lengthens rapidly and a row 

 of several cells is formed below the archesporium; these cells were 

 often seen in mitosis^ but the archesporium was never found dividing 

 until the mother-cell stage. In flowers just opening the spirem of 

 the mother cell is formed, and the synapsis stage is usually reached 

 by the time the flower is in full bloom (fig. i). While the dinsion of 

 the mother cell appears to be of rather long duration in most plants, 

 it seems to be unusually prolonged in orchids as compared with other 

 herbaceous plants. Certain cultivated orchids examined suggest the 

 probabiHty of no further development of the ovule unless poUination 

 takes place. The cells of the ovule are all relatively large, with large 

 nuclei, but the mother cell is quite striking because of its size. At 

 this stage the whole ovule, which is always very small, is growing 

 rapidly, the region of the integuments being especially active. The 

 division of the mother cell takes place in the usual way (figs, r, ij, i6). 



Certain details of this division are particularly well shown in my 

 material. After the integuments are started, the spirem begins to 

 thicken, the chromomeres are very distinct, and the thread is quite 

 long, so that it is hardly possil)le to do more than suggest its appear- 

 ance in a drawing (fig. 2). A nucleus Hke that in fig, j, in which only 

 a few threads arc drawn, shows them beginning to be paired; a little 

 later stage is shown in fig, 4, where the threads lie closer together and 

 pairing is more evident, the whole spirem being in this condition. 

 In this stage the chromomeres were not so distinct, but it was evident 

 that the threads were not entirely homogeneous. When the threads 

 have approached each other until the chromomeres almost touch, 

 or even seem to be in contact, the synaptic knot begins to form (fig. 5), 

 usually around or close to the nucleolus, which often shows vacuoles 

 at this time. As the threads are crowded more and more into the 



