65 



Dr. Wolf (1912 a, pp. 124-7), who gives some 

 good figures relating to this disease, mentions 

 that new infections may ocevu- on the segment 

 regardless of its age, entry of spores probably 

 taking place through the stomata. 



Mould. 



Professor Hammond, of the New Mexico 

 Agricultural College at Mesilla Park, referred, 

 during an interview, to the presence locally of 

 a black mould, a Phycomycete, which caused 

 damage to 0. arborescens, one of the Cylindro- 

 puntias. 



Diseases op Uncertain Origin. 



In addition to the abovementioned diseases, 

 there are some others whose cause is not known. 

 Dr. Griffiths informed the Commission that in 

 the spring (April) in the vicinity of San An- 

 toiiio, Texas, after a period of vigorous growth 

 followed by a stretch of cold wet weather, prickly- 

 pear plants may lose 70 per cent, of their joints, 

 but he could not suggest a satisfactory explana- 

 tion. He has referred to it in one of his publica- 

 tions (1908a, p. 30). 



Gumming. — A Gummosis was seen frequently 

 in South-Eastern Texas, where it did not appear 

 to be accompanied by either fungoid or insect 

 injuries. In other parts of the United States 

 onfe often ijieets with gumming associated with 

 the activities of the larvae, and occasionally adults, 

 of certain beetles (Gerstseckeria and Moneilema) 

 and moths (Melitara), But in the Brownsville 

 area definite insect injuries were not found to be 

 connected with the condition, though in some eases 

 there seemed to be indications of bug punctures. 

 Near San Antonio, gumming was seen to occur 

 along the extremities of 0. monacantha (culti- 

 vated) and 0. lindheimeri. In some cases no 

 other condition was found to occur along with it, 

 though ia others either Glceosporium disease or 

 " scald " might be present. A casual microscopic 

 examination failed to reveal the presence of any 

 organisms in the exudation, which was found to 

 be confined within the plant to certain vessels of 

 the vascular bundle. 



In the Brownsville district the gummosis v/as 

 seen more commonly and was associated with 

 other maladies. Its earlier stages could be 

 detected by the presence of small disc-like swell- 

 ings whose yellowish colour showed through the 

 translucent overlying tissues. On puncturing 

 them, a quantity of yellowish-white gummy fluid 

 oozed out quite readily. These apparently burst 

 under certain conditions, the wounded area 

 becoming infected by various organisms, Glceo- 

 sporium being one of them. M)oisture seemed to 

 favour the malady. Certain species, e.g., 0. 

 robusta and its allies, appeared to be more sus- 

 ceptible and to be more injured by the succeed- 

 ing infection, death of the joints occurring in 

 many eases observed, as ja. result of the rot which 

 set in. 



In some instances very early stages were 

 found in which the first indication seen in section 

 was the presence in the central tissue of the joint 

 of a watery-looking isolated area. The normal 

 parenchyma became converted into a clear trans- 

 lucent tissue which degenerated into a gum-like 

 substance, the latter being surrounded and limited 

 by a well-marked callus formed by the surround- 

 ing plant-tissues. The central parts of the dis- 

 eased area became brown. When the gum was 



able to exude, the injury was slight, and the part 

 healed over or else a cavity formed and the 

 progress of the disease was arrested. The gum 

 after escape hardened and commonly blackened, 

 a.s a result of the attacks of saprophytic fungi. 



Sometimes the swellings were very consider- 

 able, and suggest those described by Messrs. 

 Hunter, Pratt, and Mitchell (1912, p. 25) as 

 being caused by the presence of the larva of a 

 moth, Melitara junctolineella. Since it appeared 

 to be quite local on the plant, it is suggested that 

 this gummosis, which was insufficiently investi- 

 gated, may in part be due to the introduction of 

 some ferment by a plant bug. It may, in part at 

 least, be due to excessive root pressure during wet 

 seasons, as the so-called " fat pear " is. The 

 Commission saw cases of the latter in South- 

 Eastern Texas, the segments being considerably 

 swollen in their mid-region. The fact that 

 escape of the excess of fliiid is generally followed 

 by a return of the plant to a healthy condition 

 tends to confirm this opinion. 



Many fungi, some of which are said to be 

 pathogenic, other than those referred to above, 

 have been recorded from North American 

 Opuntias. These have been listed by Parlow and 

 Seymour (1888, 1891). One of us has already 

 published an extended list (Tryon, 1911, p. 

 16-17). 



DESTRUCTION BY RODENTS. 



It was noticed that in certain districts in 

 Texas, e.g., near Alice, Brownsville, and Sinton, 

 more or less damage had been done to species of 

 Opuntia by a so-called " blue rat " or " wood 

 rat, ' ' more commonly known locally as the ' ' pear 

 rat." A captured specimen has been identified 

 for the Commission by Mr. V. Bailey, of the 

 United States Bureau of Biological Survey, as 

 Neotoma micropus, Baird.* 



The " house " is a characteristic structure 

 piled up around the roots of an Opuntia or of 

 a mesquite tree {Prosopis glandulosa) , and con- 

 sisting of a mass of dead twigs and prickly-pear 

 debris such as fibre, spines, and dead joints. In 

 addition one may notice the presence of cotton, 

 horse and cow dung, and any available rubbish. 

 The mound varies in height from a few inches 

 up to three or four feet, and may be a few feet 

 in width. Below the " house " is an excava- 

 tion which may be roofed over with earth or 

 debris to form a tunnel with several entrances, 

 and it is in this chamber that the nest is located. 

 The latter is carefully lined with grass or 

 mesquite leaves, though other plants and even 

 cotton wool may be used as well. In order to 

 still further protect the rat against its numerous 

 enemies such as hawks, owls, snakes, and 

 carnivora, prickly-pear spines may be strewn 

 around and above the entrances as well as for 

 a short distance along the paths leading to the 

 " house." At Brownsville and elsewhere, it was 

 noticed that the animals had carefully gnawed 

 around the areoles of certain spiny species m 

 such a way that the spine clusters were removed, 

 and these were then distributed around the 

 entrances to the nest so as to afford an efficient 



* Although these rodents are spoken of as "rats," 

 and are included in the Muridae, their habits, as stated by 

 Mr. Bailey (1905, p. HI), are quite different jrom the 

 animals to which the term rat is generally appLed These 

 wood rats are very clean and feed on vegetable food. 

 Their flesh is said to be very good eatmg. 



