COMPAKATIYL CULTURAL DATA. 89 



than in solutions Lacking sugar or some nutricni equally assimilable. 

 In these cultures the quantity of conidia produced increases enor- 

 mously, often becoming a layer over the whole surface of the colony 

 half a millimeter or more in thickness. The presence of such masses 

 of spores greatly complicates the stud} of the structure of the colo- 

 nies, hut is especially characterisl ic of such species. 



THE GROUPING OF SPECIES. 



Analysis of the cultural tables presented in the light of many series 

 of comparative cultures makes possible the grouping together of par- 

 ticular races or species which possess common cultural characters. 

 It is comparatively a simple matter to single out first the unique 

 forms those which are never green, those which produce a particular 

 form of sclerotia, those which regularly produce prominent coremia, 

 or those which produce striking colors in the substrata, even those 

 associated with particular substrata. There remain, however, the 

 Large number of green forms which lack these striking characters. 

 This large group comprises probably most of the forms which have 

 masqueraded under the name P. glaucum. Lines of differentiation 

 among these forms are more or less obscure. Kept in continuous 

 culture races are easily differentiated with the eye by shades of color 

 or habit, but characters of easily recognizable diagnostic value in 

 written descriptions are more difficult to find. Inspection of cul- 

 tural data shows, however, that there is a well-marked group of these 

 forms which are able to ferment lactose as well as cane sugar. These 

 comprise the cdmemberti group (Nos. 5, 6, 39), the chrysogenum 

 group (Xos. 25, 26, 35, 44), and what we may call the "commune" 

 group (Xos. L'L\ I'.'!, 40). Among those not causing an acid reaction in 

 lactose cultures is a series of rapid liquefiers of gelatin which have 

 many characters in common (Xos. 12, l.">, LM. i!7, 3S). All of these 

 forms show special adaptability to growth in cane-sugar media. No. 

 L5, P. dtrinum, produces brilliant lemon color, especially in sugar 

 media; No. 38 is given as P. atramentosum, from its blackening of 

 the substrata in sugar media and in milk; No. 37 by developing green 

 color when sugar is present, which color is Lacking or evanescent with- 

 out sugar. These forms differ in their color reactions in the medium, 

 in the size ami shape of their conidia, in the length and origins of their 

 conidiophores, and in the arrangement of the elements in the conidial 

 fructifications. 



Another marked habit difference which holds t rue throughout many 

 series of cultures is the tendency of colonies of certain species to 

 spread rapidly over the whole surface of the substratum, whereas 

 others are quite restricted in their habit of growth. ]\\ the first the 

 developing margin is almost uniformly broad and while growing 

 white, e. g., P. roqueforti, P. italicum, P. chrysogenum, P. divaricatum, 



