OBSERVATIONS ON FLOWERING PERIODS OF CERTAIN CACTI. 39 



except when close examination is resorted to, into believing that 

 the flowers of these cacti open in the morning, as many flowers 

 may be seen in the earlier hours, if the conditions are favorable, 

 which at a distance look fresh. Observation will show, however, 

 that they are the flowers of the previous afternoon. 



Of other cacti, there have been noted several that behave 

 similarly to Opuntia fulgida. 0. mamillata has just the same 

 behavior. 0. tesselata open at about 1 :30 sun time, 0. tetra- 

 cantha about a half hour earlier. These data are approximate 

 only, as I had no opportunity to do more than determine the fact 

 that they are afternoon bloomers. 



Among all the forms I have examined the species of Echin- 

 ocactus are most unwilling to respond to illumination. On 

 cloudy days the flowers, which normally open early, are slow to 

 respond. Aside from such irregularities as I have mentioned, 

 there are therefore three types of cacti, distinguished by their 

 diurnal flowering periods. 



1. Those which flower early in the morning, at or a little 

 later than sunrise, Platopuntiae, Opuntia spinosior, 0. versicolor, 

 Mamillariae, Cereus giganteus, C. fcndleri, etc. The large, 

 beautiful flowers of Cereus pedinatus open at about 7 :00 and 

 are fully expanded in a half or three-quarters of an hour. The 

 more evanescent types, such as this species, commonly close under 

 the hot mid-afternoon sun. 



2. Those which flower at night. Cereus greggii, C. thur- 

 heri, and several others, some of which are well known in culti- 

 vation. 



3. Those which flower in the earlier half of the afternoon : 

 Opuntia fulgida, 0. mamillata, 0. tesselata, 0. arbuscula, 0. 

 tetracantha, 0. biglovii, and probably some others. 



The observation recorded in Kerner's Natural Historv of 

 Plants are more or less at variance with this classification, but the 

 behavior of the cacti at home accords well with it. It must be 

 remembered that much of our information has been gathered 

 from plants under the special conditions of cultivation. 



