Plant Growth and Vegetation. 



5 



parsley, celery, lettuce, radishes, smooth peas, spinach, and 

 cabbage with the allied forms of this species grow either wholly 

 during the cooler months of the year, or at least are at their 

 best at this season. So far as growth and resistance to low 

 temperatures is concerned, they, also, resemble t he winter 

 annual group of plants. ♦ 



The summer annual flowering plants which grow success- 

 full}' at the lower altitudes without protection are less numerous 

 than those already noted for the winter season; their best repre- 

 sentatives are globe amaranth (Gom phrena) , Prince's feather 

 (Amaranthus sps.), rose moss (Portulaca) , marvel of Peru 

 (Mirabilis), Cosmos, Petunia and Zinnia, besides numerous 

 species of morning glories. The vegetables that are least 

 affected with the heat during the summer months are beans, 

 corn, Chile pepper, eggplant, tomato, okra, melons, cucumbers 

 and squashes. 



On account of temperature conditions it would be as im- 

 possible to grow successfully the annual flowering species noted 

 immediately above during our winter months as to grow the 

 list of annual flowering plants referred to as winter growing 

 species during the summer months; and this also holds tru2, 

 as is well known, for the lists of vegetables. In this connection, 

 the writer's experience gained from a small grass garden on the 

 University grounds at Tucson, may be cited; seeds of such 

 species as timothy, red clover, red top, English blue grass, reed 

 canary grass, perennial rye, also fescue, wheat and brome 

 grasses, together with grasses in general from the Northern 

 states, when sown in the early spring, made a good growth until 

 May or June after which the seedlings were killed out with the 

 intense heat, even with reasonable irrigation; whereas when 

 seeds from the same lots were sown in the fall a good growth 

 obtained for the most part during the winter and spring season, 

 a number of the species maturing seeds before the extreme heat 

 of summer. In concluding this part of the discussion it will be 

 very interesting to observe that the plant families to which 

 our native winter annuals belong are with very few exceptions 

 the same as the introduced winter-growing flowers and vegeta- 

 bles heretofore noted are members of; and the same thing is 

 true for the families of plants representing the native summer- 



