EVERGREENS OF COLORADO 9 



pollen grains, with which the air is at this time filled, are caught upon 

 these scales and slip downward, thus coming in contact with the ovules 

 at the base. This constitutes the process of pollination. Soon after 

 the pistillate cones have been pollinated, the pistil scales close together 

 tightly to await the process of fertilization. Fertilization in the mem- 

 bers of the pine family is similar to that in other plants, except that it 

 is much slower in some of them. During this process, the pollen grains 

 that have come in contact with the ovules each send out a microscopic 

 tube which finds its way through a minute opening in the coat of the 

 ovule. In this way the cell contents of the pollen grain is enabled to 

 unite with the contents of an egg cell within the ovule. From this union 

 an embryo plant is formed, and the ovule develops into a seed. 



In the spruces and firs the cones are full grown and their seeds are 

 mature at the end of the first season after blooming. But in the pines 

 the cones make but little growth during the first season, but grow 

 rapidly during the second summer and mature their seeds at the close of 

 the second season after blooming. 



In the junipers the pistillate scales, which are few in number, be- 

 come fleshy and grown together as they mature and thus form the berry- 

 like fruits characteristic of these plants. 



The pine family in Colorado contains at least thirteen species which 

 grow to the stature of trees, while two more are merely shrubs. These 

 are grouped into five subdivisions or genera which may be distinguished 

 from each other by the characters given in the following key. 



Coniferae PINE FAMILY. 

 Key to the Genera Found in Colorado 



I. Foliage leaves needle-shaped, single or in bundles of two to five; fruit 

 a dry, scaly cone; seeds usually furnished with a thin wing. 



1. Needles (leaves) in tufts or bundles of two to five, surrounded at 

 the base by a small sheath of thin scales and placed just above a 

 little scale-like leaf or bract; scales of the mature cones thick, 

 hard and woody. 



1. Genus Pinus The Pines. 



2. Needles (leaves) single, without a sheath at the base, not seated 

 just above a bract; scales of the mature cones thin, leathery or 

 papery. 



A. Needles (leaves) in our species stiff and four-angled, each 

 one jointed to a small, hard, brownish, stem-like base; 

 branchlets from which the leaves have fallen rough with the 

 leaf-bases which remain after the upper part has fallen off; 

 mature cones hanging or pendulous, the scales persistent. 



2. Genus Picea The Spruces. 



B. Needles (leaves) flat, falling entirely away and leaving 

 small rounded scars on the branchlets, which are quite 



smooth after the needles have fallen. 



