Jtdy 3, 1879] 



NATURE 



225 



shorter than the men. There are, in fact, only three 

 other races which are equal or approximate to them in 

 smallness, viz., the Bushmen, the inhabitants of Tierra 

 del Fuego, and the Lapps. The name of Mincopie has 

 often been applied to these people, but it does not appear 

 to be now used in the islands. 



(To be continued^ 



ON POLLEN PLANTS 



THE evolution of the vegetable cell— using the word 

 evolution as defined by Herbert Spencer — is a 

 subject of immense interest that is now engaging the 

 attention of some of the most scientific of the botanists. 

 While the important researches of Carl Nageli on cell- 

 structure and cell-development can never be over-esti- 

 mated, yet in these more recent times we are greatly 

 indebted to the original and remarkable researches of 

 Eduard Strasburger, which have thrown a flood of light 

 on the subject, and opened out for it new and as yet 

 untrodden by-paths. His thoughtful work, " Ueber 

 Befruchtung und Zelltheilung," ought to be in the hands 

 of every student. It is not here purposed to analyse the 

 contents of this volume, now more than eighteen months 

 on our shelves, but in it, we fear somewhat overlooked, 

 we find the subject of the cellular- structure of the " pollen 

 grains" in the angiosperms first mentioned, at least, in 

 very recent times, and we are glad to perceive that the 

 facts relating thereto have been recently restudied, and in 

 some detail, by Fredr. Elfving, of Helsingfors, under the 

 eye of Strasburger, and in his physiological laboratory at 

 Jena. 



We adopt for convenience the ordinarily received division 

 of plants, in which the flowering plants, or those having the 

 sex-cells developed in connection with phyllomes, are 

 separated from the so-called flowerless plants, in which 

 the se.x-cells are formed on thallomes. All the more 

 recent manuals of botany assert that the two groups of 

 the former, the gymnosperms and the angiosperms, are 

 differentiated, the one from the other, by certain striking 

 peculiarities relating to their reproductive systems. One 

 of these is that in the former the pollen-grains are multi- 

 cellular, and that in the latter the pollen-grains are uni- 

 cellular, a nice, and it ought to be an easily ascertained dis- 

 tinction, but unfortunately one that turns out on investiga- 

 tion not at all true. In the pollen-grains, or, as we would 

 prefer to call them, the pollen-plants of the gymnosperms, 

 there are all the essentials of an adult and independent 

 form, that is to say, the protoplasmic contents of the pollen 

 plant divide into two or more cells, of which one takes upon 

 itself the growth and functions of the pollen tube, and the 

 other remains with no such functional power, but at most 

 plays the feebler part of a vegetative cell. There is thus, as 

 it were, a thallus formed, one cell of which performs the 

 function of an antheroidal or male cell. All this has been 

 for some time known to be the case in the gymnosperms of 

 which our cone-bearing trees and shrubs may serve as 

 familiar types ; but in the angiosperms, embracing nearly 

 all our showy flowering herbs, shrubs, and trees, despite 

 Strasburger's researches published in 1877, it is still most 

 generally stated that inside the inner coat of the pollen- 

 grain there is but a single protoplasmic mass which gives 

 rise to the pollen tube. So far as this difference in the 

 pollen goes, it will now probably not be again insisted on, 

 for a glance at the very copious figures drawn from nature 

 by Mr. Elfving will satisfy the most sceptical that the 

 angiospermous pollen-grain is really a compound body, 

 entitled to rank as a thallus, and in which, as in the 

 gymnosperms, there are both functional and vegetative 

 cells. The researches culminating in this memoir wjere 

 chiefly made during the summer session of 1878 in the 

 Botanical Institute at Jena. The pollen was cleared 

 by means of a i per cent, solution of osmic acid, 

 ftnd then stained and preserved in a carmine-glycerine 



fluid. If the outer coat be not too dense, the con- 

 tents can be seen through it after from one to two 

 days' steeping in osmic acid. In order to see the 

 growth of the pollen tube, recourse must be had to arti- 

 ficial culture ; for this purpose many sorts of solutions 

 were used, and these of very different degrees of con- 

 densation, but in the end the author came back to a 

 simple solution of i to 25 per cent, of sugar. Some 

 pollen plants required but weak solutions, others strong 

 ones. The strength of the solution found in certain cases 

 most useful is given in the details of the experiments. 

 The culture upon most were generally made in the dark, 

 and at a summer temperature, but some grown in daylight 

 succeeded admirably. The orchids are referred to as 

 affording most excellent subjects for these investigations. 

 On three plates the different forms of pollen-plants to be 

 met with in some twenty-three species of plants are re- 

 presented. Of these we select that of Tulipa gesneriana, 

 in which the vegetative cell happens to be very large 

 (a in figure), and it very frequently divides, as seen at B, 

 also that from BtUomns umbellatus (c), showing the 



vegetative cell and the tube. In this figure the side 

 walls are not represented. The chief results of these 

 researches are collected together as follows : — The pollen- 

 grain in the angiosperms becomes divided into two cells, 

 generally a larger and a smaller one; the latter, the 

 " vegetative " cell, by a further division, becomes deve- 

 loped into a two- or often a three-celled thallome. This 

 vegetative cell, or these vegetative cells, are only sepa- 

 rated from the larger cell by* a wall of cortical plasm, 

 (ectoplasm, Vines), but this, in particular instances, can 

 become formed into a firmer membrane (cellulose .'). The 

 pollen tube is the result of an outgrowth of the larger cell. 



In the gradual growth of this it may happen that the 

 vegetative cell or cells will wander into the pollen tube, 

 the wall of the larger cell having become obliterated, or 

 they will remain free in the cavity of the mother-cell, often 

 becoming spindle or half-moon-shaped. 



The nuclei are often peculiarly fashioned, but with the 

 exception of the Cyperaceae no instance of a division of 

 the nucleus of the larger cell was observed. 



All the pollen plants described by Elfving belong to the 

 sections either of the "wind-wafted" or the "insect- 

 borne " forms. The study of the structure of the pollen 

 plants of such cleistogamous flowers as those recently 

 described by Bennett, such as some of the violets, wood 

 sorrel, &c., may reveal some interesting facts. In them 

 there would seem to be a greater individuality ; the very 

 behaviour of their pollen tubes is so different that they would 

 appear as if they had a more independent basis ; but this is 

 rather a subject for research than for conjecture. In the 

 meanwhile we may note how many apparently sure land- 

 marks have been, in the botanist's country, lately thrown 

 down by the researches of Warming, Strasburger, and 

 now Elfving. It will be difficult by and by to invent neatly- 



