MILDEWS. 43 



And just here, allow me a parenthesis. The accurate statement 

 of scientific facts or conclusions requires the use of scientific 

 language. The vocabulary of any science includes familiar words 

 used in a technical sense, and speciall}" coined words. For these 

 technical terms science has no apologies to offer ; their use is the 

 inevitable condition of accurate thought or statement, and whoever 

 would become intelligently familiar with scientific methods or 

 conclusions must be prepared to accept and adopt them. They 

 give to thought and statement a definiteuess most attractive 

 to the precise mind, if it is the dread of the slipshod thinker. 

 The layman may justly ask that these terms be clearly and 

 thoroughly explained when thej' are first used, but the botanist 

 may as justly feel free to use them after they have been so 

 explained. Their seeming difficulty is only in their unfamiliarity, 

 which is soon overcome. 



The word plant calls to the mind of the average hearer the idea 

 of a living organism growing in the earth, in which it is held and 

 from which it draws water by means of roots^ and having a stem 

 above ground, on which are borne leaves. But this idea is an in- 

 complete one ; because probably a half of all known plants do not 

 answer to this description at all. Most of the so-called higher 

 plants, it is true, are composed of these fundamental organs — root, 

 stem, and leaf — each of which has its special functions, and they 

 may be designated Stem-Plants. Contrasted with them however, 

 is an immense number of so-called lower plants in which there is 

 ■comparatively little dift'erentiation into special organs, and there- 

 fore little division of labor. In these simpler plants, the whole 

 plant-body is known as a thallus and the}' may be termed Thalhts- 

 Plants. Typical examples are the "rock weeds" and "sea 

 mosses " of our coast. Again, greenness of color is commonly asso- 

 ciated with the idea of a plant ; but this too is not a constant 

 character. It is true some parts of the typical plant contain a 

 green pigment which gives them their color ; and it is this sub- 

 stance, called leaf-green or chlorophyll., which gives to green 

 plants their power of preparing the complex organic compounds 

 which serve as their food-material, from inorganic constituents 

 taken from the air and soil. But cases are familiar of stem-plants 

 which are without chlorophyll. Such, for instance, are our com- 

 mon Indian Pipe and Dodder, which must live on food-material 

 elaborated by other plants. It is however among the thallus- 



