CACTUS SPINES AND PECULIARITIES 31 



growth; and if all these areolas are cut away on the stem and 

 its tip cut off, tiie plant ceases to grow and dies. Spines are 

 generally understood to represent branches, since they grow 

 from the tissues of the plant under the epidermis and not 

 from the epidermis. The inordinate multiplication of 

 spines in cacti is not well understood by botanists. Some 

 cacti add thorns to their spine clusters in the areolas each 

 year, and thus in time the cluster may come to have as many 

 as fifty or even a hundred spines on old stems and large 

 branches. Occasionally cactus spines replace themselves in 

 areolas after the former thorns have been destroyed or 

 burned off. The thorns of some cacti may grow as long as 

 six inches and even longer, and as broad as one-fourth inch at 

 their bases. After they complete their growth toward the 

 close of the season and the bases become hard and firm, they 

 do not elongate farther nor make further growth. 



The flowers of cacti are generally large and showy and 

 are quite responsive to light in their opening and closing. 

 They have many stamens, from thirty or fifty to as many 

 as three thousand in the Giant Cactus. This development 

 of stamens is rare among flowering plants, and is due to a 

 splitting process that takes place early in the development of 

 the stamens of the embryo flower. The stamens of many 

 cacti are sensitive to touch and when being worked by insects 

 for pollen are constantly moving backward and forward. 

 Cactus flowers differ also from nearly all other flowers in the 

 number of sepals and petals, which is variable and relatively 

 large, and in the fact that their sepals and petals are not 

 distinct in character. Rather there is a gradual transition 

 between the bracts of the ovary, if such are present, and the 

 sepals; and likewise a gradual gradation in form, color, and 

 size between the sepals and petals. There are usually sev- 

 eral whorls or circles of petals in the flower; commonly such 

 flowers are spoken of as being double. 



