62 



NATURE 



[March r8, 1909 



more than 7° C, few roots or leafy shoots are formed, 

 but new tubers develop readily, though, of course, 

 remaining small. If the parent tubers are then culti- 

 vated at 25° C, leafy shoots are freely formed, the 

 younger tubers of the new growth often being con- 

 tinued into leafy shoots at the tip. 



The relations between leafy shoots and inflorescences 

 are discussed as conditioned by the relative amounts 

 of organised and mineral supplies to each; and the 

 well-known effects on trees of root-pruning and over- 

 feeding are brought under the general law. Certain 

 plants [e.g. Veronica Beccahunga) show that their 

 inflorescences may readily be caused to grow into 

 leafy shoots. Space will not permit of more than 

 a passing reference to the very interesting discussion 

 of the changes that can be induced in the colours of 

 certain flowers and the structure of others by altera- 

 tions of environment and food and of the conditions 

 under which cleistogamous flowers are normally pro- 

 duced. The production of buds in abnormal situa- 

 tions, either as a usual occurrence, as on the leaves 

 of Cardamiiie prateiisis in autumn, or following the 

 partial or entire separation of the part from the plant, 

 so largely utilised in the multiplication of begonias, 

 hyacinths, and certain other plants, is treated at 

 considerable length, and is summed up as closely 

 akin to regeneration, both being especially active at 

 the growing-points of axes or leaves ; but adult tissue 

 in certain areas may revert to the embryonic state, 

 these areas being along the veins ; and the impulse to 

 development, apart from external stimuli, is con- 

 ditioned by the presence of the necessary constituents 

 of the food, brought about in leaves, when the petiole 

 is cut or broken, by the retention of the leaf's products 

 within itself. The book, though not large, does not 

 lend itself to a brief review, as it is conspicuously free 

 from irrelevant or useless matter. The student will 

 find in it much information of high value, and much 

 to suggest new aspects of the life of plants and of 

 how experimental methods may be usefullv employed 

 in the search after the laws that govern them. 



(2) Dr. Winkler's work on parthenogenesis and 

 apogamy is one of the excellent monographs that have 

 rendered " Progressus Rei Botanicae " indispensable 

 in every botanical library. It deals with one aspect 

 of the activity of protoplasm, as manifested in repro- 

 duction of the species by methods very different in 

 some respects from the normal, and the possibility of 

 which w-as scarcely suspected until comparatively re- 

 cent years. But though of recent development, this 

 field of research has had much attention directed to 

 it, and a copious though rather scattered literature 

 has appeared, rendering this review of the whole 

 field most timely and helpful both in itself and as 

 a guide to the original papers. It is no mere com- 

 pilation, but is an excellent contribution to a diffi- 

 cult subject. A brief sketch of the history of the 

 discovery of the methods of reproduction in plants 

 up to the recognition of true sexual reproduction as 

 normal in them forms an introduction to the later 

 history of the discoyeries that in some plants the 

 se.xual method is not followed, that the embryos 

 result from a vegetative growth of some other cell 

 NO. 2055, VOL. 80] 



or cells than the ovum, and that the unfertilised ovum 

 may develop as an embryo. These abnormally pro- 

 duced embryos have been studied in their origin 

 and growth in numerous species (from widely dif- 

 ferent groups of plants) both as they occur naturSIlv 

 and as they result from external stimuli, such as 

 injuries to the parts that produce them, various salts 

 in solution, or differing concentration of food-solu- 

 tions. 



The terminology in use for these methods of re- 

 production has varied as employed by different in- 

 vestigators, and the terms are reviewed and defined 

 clearly. The methods of production of new individuals 

 are recognised as of three types, viz. a)}ipliimixis, 

 the embryo resulting from the union of two clearly 

 distinct cells, the ovum and sperm, or their equiva-' 

 lents, this being true sexual reproduction ; pseitdo- 

 mixis, the embryo being developed, directly or in- 

 directly, from a union of two cells not the equi- 

 valents of the ovum and sperm, as has been obser'ved 

 to occur in certain ferns (in which a cell of a pro- 

 thallus after entrance into it of the nucleus of a 

 neighbouring cell, and union of the nuclei, produces 

 a new fern plant), and probably also in the reproduc- 

 tion of various fungi (while similar nuclear fusions, 

 unconnected with reproduction, have been found to 

 occur as an effect of chemical agents, e.g. of chloral 

 on roots of Vicia) ; and apomixis, where the produc- 

 tion of the new individual has not been preceded by 

 fusion of nuclei, either sexual or asexual, and is 

 evidently asexual. 



The term apogamy was first used by de Bary (in 

 1878) to signify the replacement of sexual reproduc- 

 tion by any other method, i.e. as almost equivalent 

 to apomixis; but it has been used by others with 

 meaiiings a good deal different from this. Dr. 

 Winkler therefore defines his own use of the terms, 

 thus : — -Apogamy is the apomictic formation of sporo- 

 phytes from vegetative cells of the gametophyte ; 

 Parthenogenesis is the apomictic formation of a 

 sporophyte from an ovum. Each is distinguished into 

 two types by the number of chromosomes in the 

 nuclei of the cells giving origin to the new plants, 

 viz. somatic with diploid, and generative with haploid 

 nuclei. With these restrictions, the conditions that 

 lead to, or favour, the occurrence of one or other of 

 these modes of reproduction, their relations to the 

 more usual sexual and asexual types, and their bio- 

 logical significance are treated in a very full and 

 thorough manner, supplemented by a bibliography in- 

 cluding 239 titles. 



Before describing more fully the ascertained cases 

 of apogamy and parthenogenesis, a careful analysis 

 is made of many recorded cases in which the condi- 

 tions are uncertain, or too insufficiently observed to 

 allow of determining to which type thev belong. 

 Among these are examlpes of alg« such as Proto- 

 siphon, shown by Klebs to be capable of facultative 

 parthenogenesis, or of iinibn of gametes, under de- 

 finite changes of food-solution or of temperature, but 

 in which thie number of the chromosomes in the 

 plant developed in each case has not been ascertained. 

 Other cases insufRcreiitly determined in this respect 



