December 1, 1898.] 



KNOWLEDGE. 



285 



and tbe picturesqueness, and settle down to work on the 

 eagential parts of the flower. 



First, the Stanitns. The two anther-saos with their 

 yellow dust-like pollen recall at once the pollen-aaos of the 

 pine, and if we were right in regarding those as micro- 

 sporangia, there is no reason why we should not use the 

 same term here. The stamens are, in fact, " micro- 

 xpiiroji/iylls," or microspore-bearing leaves ; the anthers, 

 micrusporanijiii, and the pollen-grains microspori-s. Thin 

 transverse sections of the anther can be easily made for 

 the microscope, and there is no difficulty in observing the 

 two-layered wall, and the four enclosed chambers. 



In ripe anthers the chambers will contain loose pollen- 

 grains, but in those in the immature stage, the pollen- 

 grains will be seen developing in groups of four by the 

 division of a single " mother-cell," thus resembling the 

 microspore formation in Selaginella. The ripe pollen - 

 grains appear to consist of a single cell, and if they are 

 stained and mounted, it will be found that such is the 

 case ; but there are tu-o nuclei, a fact of great interest when 

 we remember that the pollen-grains of the pine h;id also 

 two nuclei, one of which was contained in a special cell, 

 separated by a wall from the rest of the cell-contents. 

 This we regarded as equivalent to the group of cells in the 

 Selaginella microspore, a rudimentary male prothallua. 

 Here, though no cell-walls are formed, we cannot help 

 looking on the second nucleus as the last relic of the 

 vanished prothallus. 



The apical part of the flower we find occupied by an 

 elongated, slightly three-sided structure, the uvartj. A 

 cross-section of this shows it to contain three chambers, 

 each with a double row of ovules growing from the central 

 column formed by the meeting of the three division walls. 

 Though it may not appear so at first sight, the whole is 

 really composed of three specialized leaves, the carpels or 

 macrosporoiiliijlls. If we imagine a scale like that of the 

 pine cone to bear a row of ovules along each side-margin 

 and then to be folded down the middle so as to bring the 

 two rows of ovules together, a single-chambered ovary 

 would be formed such as is seen in a pea-pod. If, however, 

 there were three carpels placed like the sides of a triangle, 

 and these were all similarly folded, with the inturned 

 walls in contact, a three-chambered ovary like that of the 

 lily would result. The carpels are, in fact, sporophylls, 

 each with a row of macrosporangia along the margins, 

 and the three compacted together in this manner form the 

 ovary. 



By cutting a number of sections across the whole ovary 

 it is probable that one of tlie sis possible ovules in each 

 slice will be cut near the middle plane, and the following 

 structures can then be observed. 



There is a central tissue mass, the nucellus, but it is 

 enclosed in this case by a douli'i intefjumint which is 

 absent at the apex, leaving, as before, a little passage or 

 iiiicropijle. As in the pine, also, there is a large oval 

 embryo-sac or macrospore, lying in the nucellus ; but here 

 we find important differences between the present type and 

 the conifer. Instead of containing a mass of cells, the 

 "prothallus," the sac here contains protoplasm, with large 

 fluid " vacuoles." A large nucleus will be seen near its 

 centre, and there is a group of three round nucleated cells 

 at each end of the sac. The group of three, at the end 

 furthest from the micropyle, called the " antipi'ihit cells," 

 must be regarded as the last trace of a prothallus tissue. 

 The group at the opposite pole consists of two small cells 

 side by side, close to the apex of the macrospore, and 

 below the mic/opyle ; and a third larger cell below them. 

 Its position would suggest that it corresponds to the eriy- 

 cell of the pine-ovule, and observation of the fertilization 



process proves this to be the case. During this process 

 the two smaller cells, or sijnerijiils, are inactive, and they 

 seem to have no special duty to perform, so that we are 

 perhaps safe in regarding them as the last relics of the 

 neck of an archegonium. 



When the pollen-grains have become attached to the 

 stigma they throw out pollen- tubes, which grow down 

 through the tissues of the style till they reach the neigh- 

 bourhood of the ovules, and their tips pass through the 

 micropyle. The end of the tube at this stage may be seen 

 to contain two or three nuclei, but it will be found that 

 only one of these is the fertilizing agent. When the end 

 of the tube is in contact with the macrospore its end wall 

 is absorbed ; the active, or sperm-nucleus, passes in and 

 fuses with egg-nucleus, but the other nuclei in the pollen- 

 tube remain passive. This, of course, tends to support 

 the view that they represent the merely vegetative cells of 

 the ancestral prothallus. 



After fertilization the embryo-sac becomes filled with a 

 tissue of cells serving for nourishment for the embryo 

 plant, and this tissue is known as the emlosprrw. From 

 its formation at this stage, however, it is evidently a 

 different thing from the endosperm in the pine, which is 

 the macrospore-prothallus. 



At this point we must leave the story of the lily, as the 

 subsequent divisions of the compound nucleus, and its 

 gradual growth into an embryo in the seed, and finally into 

 a new lily-plant, are all matters apart from our special 

 purpose. 



What we have found is that by a careful study of the 

 minute details of the flower we can prove the presence 

 there of parts corresponding to those observed in the higher 

 flowerless plants. We have found that even in the highest 

 plants we can trace the relics of that " alternation of 

 generations" which is so characteristic of the life-history 

 of the moss and the fern. Though, from the moss upward, 

 through the series of types we have studied, the Sporophyte 

 stage has become ever more and more predominant, and 

 the Oophyte stage ever less and less, the microscope 

 shows it to be still there though hidden away among the 

 secrets of the ovule and the pollen-grain. 



NOTES ON COMETS AND METEORS. 



By W. F. Denning, f.b.a.s. 

 New Cojiet. — Mr. W. R. Brooks, of Geneva, N.Y., 

 discovered a pretty bright comet in the constellation 

 Draco at R.A. Uh. o5m. 10s., Dec. + G0° 26' on the 

 evening of October 20th. It was moving rapidly to the 

 S.E., and after travelling through Hercules, crossed the 

 equator on November 17th, and reached its perihelion six 

 days later. The comet appeared to be about 4' or 5' in 

 diameter, with very decided central condensation, and 

 about equal to a star of seven and a-half magnitude. 

 There is no reason to suppose that the orbit deviates 

 sensibly from a parabola. During the first half of 

 December the comet will be situated in the north-western 

 borders of Sagittarius, and its apparent motion will have 

 become very slow. The following is an ephemeris by 

 MoUer of Kiel for Berlin mean midnight : — 



Distance in 



