MICHIGAN ACADEMY OF SCIENCE. 157 



frequent zero weather. Deep snow prevented the ground being 

 much frozen. 



At the end of the winter only one jdant was alive, a low speci- 

 men of Maniillaria arizonica that had been well protected b.y snow. 

 All the others had been apparently killed by the first cold snap in 

 November, or, weakened by the cold, died in the warm period that 

 followed. Tlie exact time of death was difficult to determine. 



Nine species that I had carried over were established out of doors 

 in the summer of 1912. The fall was again very wet and the early 

 part of the winter wet and mild. Januarv was unseasonablv warm 

 with heavy rain storms. With February, winter really began bring- 

 ing cold and snow and the lowest temperature was in the first week 

 of March when -4 F, was reached. 



The specimen of ^Mamillaria arizonica that survived the previous 

 winter died but another plant of the same species lived and this was 

 the only survivor. Most of the others died early in the winter 

 but in some cases death seemed to have been caused by decay rather 

 than by cold. 



The last of my plants were left out this past winter. They had 

 proved their ability to endure twenty degrees of frost in the en- 

 closed porch where they had been kept the previous season. There 

 was one plant each of Maniillaria arizonica, Opuntia spinosior, O. 

 santarita and 0. leptocaulis. They all died early. 



The general conclusion from my experience is that Arizona cacti 

 will not survive Michigan winters. The most obvious of probable 

 reasons is temperature. Dr. Shreve informs me that at their 8,000 

 foot station the minimum temperature in severe winters is about +5 

 F. None of my species range above that height and most of them are 

 found considerably lower down. In Michigan a winter temperature 20 

 degrees lower than what they have to endure in Arizona would be 

 usual. But most of my specimens were dead before the minimum 

 was reached, sixteen degrees of frost being fatal to many of them. 

 In the case of those species that inhabit the lower ranges as Car- 

 negia gigantia this is not surprising, but Echinocereus polyacantha 

 ranges to 7,800 feet, Maniillaria grahami to 7,000, Oipuntia santarita 

 to 5,400, O. spinsior to 5,000, O. versicolor to 5,200. These were 

 killed by temperatures probably no lower than that they might have 

 experienced in their native habitat. It is rather curious in this 

 connection that the species which seemed hardiest with me, M. 

 arizonica, has a range up to 6,000 feet, not as high as E. polyacantha 

 or M. grahami. 



I think that the warm wet falls that are so common with us have 



