Apbil 22, 1910] 



SCIENCE 



635 



hard object, nor to continued pressure, nor to 

 release of pressure. The failure of the leaf to 

 respond to shaking is probably connected with the 

 small inertia of the sensitive hairs, and the slight 

 resistance offered by the air to their passage 

 through it. 



Water at room temperature causes closure only 

 when it bends a sensitive hair. 



After one mechanical stimulus there is a short 

 period during which a second mechanical stimulus 

 is ineffective. 



Effects of Acidity of Culture Media upon Mor- 

 phology in Species of Penicillium: Chables 

 Thom. 



Increasing recognition of the economic impor- 

 tance of saprophytic forms, such as species of 

 Penicillium, lends interest to the study of their 

 metabolic activities. Although production of cer- 

 tain enzyms determines the ability to digest par- 

 ticular forms of food, the elements necessary to 

 normal growth of any of these forms are present 

 in nearly all kinds of fruit, meat and vegetables, 

 or other food products. The presence or absence 

 of a particular species of Penicillium as an agent 

 ol fermentation or decay, is therefore determined 

 by its tolerance of other factors. Among these are 

 temperature, relative humidity of the atmosphere, 

 percentage of water in the substrata, the forms of 

 carbohydrate present, the concentration of osmotic 

 substances, and the alkalinity or acidity of the 

 media. One of the easiest of these to demonstrate 

 relates to the alkalinity or acidity of the medium. 

 The cultures shown represent a series of conditions 

 illustrating the range of this tolerance for certain 

 species of Penicillium. 



Using tubes containing 10 c.c. each of a medium 

 neutral to phenolphthalein, alkali has been added 

 as normal sodium hydroxid, and acid as normal 

 lactic acid. The change in the constitution of the 

 medium can thus be given as cubic centimeters 

 of normal acid or alkali per ten of medium. 

 Uniform volume is maintained by increased con- 

 centrations. The range of tolerance in the species 

 studied is from 2 c.c. of alkali per 10 c.c. of 

 medixim to 5 c.c. of normal acid to the same 

 amount of medium. Within this extreme range, 

 most species are much more closely restricted. 

 Very few species grow to any degree in plates 

 alkaline to phenolphthalein {P. hrevicaule and its 

 allies) . Of the very common green species but few 

 fruited freely in alkali as strong as a tenth nor- 

 mal. Nearly all grow best between the neutral 

 point and an acidity approximately equal to tenth 

 normal. The most widely reported forms show 



naturally the greatest tolerance (P. roqueforti, 

 P. expansum ) . 



The inhibiting effects of acid vary with the 

 species and with the kind of acids. The first effect 

 noted is usually the retardation of growth and 

 especially of the production of colored spores. In 

 some the retardation is temporary; again it re- 

 duces the final size of the colony. There results 

 a gradation from the normal colony to very small 

 colonies but with typical morphology. In others, 

 a concentration is soon reached which inhibits the 

 production of colored spores entirely. In others 

 the production of bright colors in the substratum 

 is partly or entirely stopped. The typical mor- 

 phology of fruiting areas is often greatly changed. 



Testing their tolerance to acid emphasizes the 

 close relationship of certain groups of forms and 

 offers a very useful accessory to the description 

 of species. Along with other cultural evidence it 

 seems to show that the presence of special forms 

 as agents of decay in certain fruits (P. italicum 

 and P. digitatum on citrus fruits), is due not so 

 much to adaptation to the fruit as a form of food 

 as to tolerance of the other substances present. 

 It should be noted that in synthetic media it can 

 be readily shown that the standard formulae 

 (Eaulin's, Cohn's, Uschinsky's, Czapek's) are ex- 

 tremely dilute and in no sense to be regarded as 

 the optimum for mold growth. In fact in solu- 

 tions of non-toxic substances much greater con- 

 centrations may be used than any of these for- 

 mulae call for and bring about correspondingly 

 greater masses of typical mold growth. The 

 responses to acidity are much more rapid and 

 radical in the character of the growth obtained, 

 hence quickly reach a diagnostic value in most 

 species. 



Effect of Various Gases and Vapors upon Etio- 

 lated Seedlings of the Sweet Pea: Lee I. 

 Knight, R. Catlin Rose and William Ceockek. 

 The effects of impurities of laboratory air upon 

 the etiolated epicotyls of seedlings of various 

 legumes have been described by a number of Ger- 

 man investigators. The effects are three : decrease 

 of rate of growth in length, swelling of the region 

 growing while exposed to the impurity and a 

 horizontal placing o*-''^gion. These investigators 

 assume that almo... aiiy gaseous impurity, even in 

 low concentration, will produce this three-fold 

 response. The accompanying table shows deter- 

 minations made with eleven gaseous impurities 

 upon the sweet pea, Earl Cromer. The horizontal 

 placement induced by ethylene, illuminating gas 

 and acetylene seems to be an induced diageotropism. 



