Observations on Mamillaria elongata. 
BY 
OTTO V. DARBISHIRE. 
With Plates XXV and XXVI. 
Contents 
A. Introduction— The Problem . 
B. Observations on Mamillaria elongata 
(1) Morphology 
(2) Anatomy 
a. The stem . . 
b. The root .... 
c. The tubercle .... 
(3) Homology of the tubercle 
(4) Physiology 
a. Introductory remarks . 
b. Physiology of Mamillaria elongata 
c. Comparison with other plants 
C. Concluding Remarks. — The Results 
Literature. — Description of Plates 
PAGB 
375 
377 
3 77 
378 
378 
381 
384 
39 3 
395 
395 
397 
405 
408 
412 
A. Introduction. 
T HE species of the natural order Cactaceae show a remarkable uni- 
formity in the plant-form they represent. From this point of view the 
genus Mamillaria may be taken as typical for its natural order. 
The Cactaceae occur in desert regions, and are thus subject to the 
influence generally of adverse conditions. The deviation which they 
represent, from what we may call the normal dicotyledonous type, makes 
a study of this order, as representing a definite plant-form, very interesting. 
This interest is heightened when we find the Mamillaria type occurring 
in another desert genus, belonging to a different natural order, namely 
in Mesembryanthemum , a genus of the Aizoaceae. Mesembryan themum 
stellatum represents a plant-form of the same type as Mamillaria 
elongata. 
In the literature of the subject very little information can be obtained 
concerning the physiology of Mamillaria, , as a definite ecological type. 
[Annals of Botany, Vol. XVIII. No. LXXI. July, 1904.] 
