191t] CURRENT LITERATURE 321 
cals that are effective are traces of illuminating gas and tobacco smoke; con- 
siderable concentrations of CO, (4-50 per cent); high partial pressures of 
ether and chloroform vapors; and HCl gas. Other effective stimuli are high 
temperatures, shaking, sprinkling with dust, and wounding the style. Frr- 
TING concludes that the process is a vital one, for it does not occur when the 
plant is in heat rigor or in rigor from lack of oxygen. He also concludes that 
it is a true stimulus process, showing well-marked presentation and reaction 
times, as well as typical summation and relaxation. The reaction cannot be 
varies greatly with the stimulus, age of flower, and species of flower. Traces 
of illuminating gas give a reaction only after 2-6 hours, while CO, in optimum 
concentration gave a reaction after 30 seconds in Verbascum thapsiforme, and 
after only a slightly longer period in a number of other forms. Reactions to 
Shaking and high temperatures were also rapid. Old flowers were always 
more sensitive than young ones. 
ITTING proposes to call these responses chorisms, using the prefixes chemo-, 
€rmo-, seismo-, etc. The paper should prove of considerable economic 
interest—WILLIAM CROCKER 
Fundamental units of vegetation.—Ecology as a definite branch of the 
science of botany, _— sult § in Wen —, has xesehied a ae its wher A 
ment at which i 
to inquire what were the bela: from which the branch has developed 
and whether there are tendencies which require pruning or molding. Moss? 
has taken such a backward look over the course of the development of the 
concepts and the nomenclature of the units of vegetation most used in the 
Study of plant communities. The look has been a careful one, and has traced 
“plant associations” from its first use in a floristic sense by Humso.pr, in 
1806, and with its truer ecological meaning by ScHouw, in 1822, to the present 
day. To Moss the concept seems to be best defined as ‘‘a community of 
definite floristic composition within a formation.” 
“plant formation” a term and concept of slightly more . recent 
origin, dating to its employment by GrIsEBACH in 1838. The different 
oe this term has had for various workers are discussed in such a manner 
as seems likely to lead to some agreement as to its proper content. The 
desirability of some general agreement as to methods of denoting associations 
and formations is discussed in a most reasonable manner, and several good 
Suggestions made. The writer is to be commended for correctness of per- 
spective and breadth of view throughout what is doubtless the best historical 
review of this phase of botany which has yet appeared.—Geo. D. FULLER. 
eee es 
*Moss, C. E., The fundamental units of vegetation. New Phytol. 9:18-53. 
IgIo, 
