62 BOTANY OF CROP PLANTS 



The "thallus plants" (Thallophytes) include the simplest 

 organisms. This group is divided into two large subdivi- 

 sions, the AlgcB and Fungi. The Algae include the green 

 scums so frequently observed upon the surface of pools, 

 stagnant ponds, reservoirs, ditches and streams. They are 

 also commonly found in tanks and water troughs, and, in 

 such places may render the water objectionable to stock, 

 especially when decay sets in. The brown and red "sea 

 weeds" are also Algae. The Fungi are a large group of 

 plants, probably the best known being the bacteria, the 

 molds of bread, fruit, and cheese, the rusts and smuts of the 

 cereals, the toadstools and mushrooms, the mildews, and the 

 fungi causing such well-known diseases as blight of potato, 

 alfalfa leaf spot, apple scab, wilt of cucurbit, etc. 



The "moss plants" (Bryophytes) include the liverworts, 

 peat mosses, black mosses, and common mosses. They are 

 a group of comparatively slight economic importance. 



The "fern plants" (Pkridophytes) are represented by the 

 true ferns, and closely allied plants such as the horsetails or 

 scouring rushes, and club mosses. Like the preceding 

 groups, fern plants do not produce seed but reproduce in a 

 much simpler fashion, by spores. 



The highest and most complex group is the "seed plants" 

 (Spermatophytes). It includes the Gymnospermce (pines, 

 spruces, firs, hemlocks, cedars, junipers and other cone-bear- 

 ing plants) and the AngiospermcR (higher seed plants or 

 flowering plants). All the common crop plants, of field, 

 orchard, and garden belong to the Angiospermae. In the 

 Gymnospermae the seeds are exposed, while in Angio- 

 spermae they are enclosed in a case, the ovary wall. Angio- 

 spermous plants fall into two groups (subclasses): (i) 

 Monocotyledpnes, in which the seeds have one cotyledon', the 

 flower parts are in threes, the leaves are parallel-veined, and 



