School of Pharmacy, University of Portsmouth, Portsmouth, Hampshire, UK
The plant Cannabis sativa has been providing man with a range of his most basic needs for centuries (Conrad, 1994a). We know that hemp—the fibrous extract of C. sativa, was used for clothing in ancient Egypt, at least as early as 1,200 years BC and the use of the plant as a source of rope is well documented in many cultures down the centuries (see Chapter 1, this volume, for a full account). The seeds from the plant have been subjected to various treatments to provide food and the fibre has also been used from early times as a major paper making material; indeed, early editions of the Gothenburg and King James Bibles were published on such paper and much later, the first two drafts of the American Declaration of Independence. The new president of the United States, George Washington was to be found exhorting his head gardener to: "Make the most of the Indian hemp seed...and sow it everywhere" (Washington, 1794).
These peaceful uses were not the only ones however. From the 17th century onwards, the British Royal Navy—at the time the most powerful navy in the world— relied heavily on hemp for ropes, rigging and caulking. In the mid-1800s, a typical 44-gun man of war might inventory some 60 tons of hemp rope, rigging and anchor cable, often impregnated with tar to improve the already excellent resistance to rotting encouraged by constant exposure to sea water; not to mention the hemp-derived oakum, forced between the planks to make her watertight. The sails were made of 'canvas' a derivation from an Arabic word for hemp. Soldiers' and sailors' clothing and their battle flags were likely to be made of hemp material also. The original 'Levi's' jeans were made from recycled hemp sail cloth and in World War 2, hemp was widely cultivated in the US and Germany performing many vital functions, from fire hoses to parachute webbing.
This chapter is not intended to be an agricultural or horticultural manual for those interested in growing the plant for legitimate commercial gain. Chapter 2 provides a fairly detailed historical account of cultivation and subsequent processing of C. sativa and the interested reader is referred to this text and its accompanying references (see also: Conrad, 1994b; Judt, 1995). For those requiring further information, references are provided in the bibliography to organisations which may provide additional advice in this area.
The reader is referred to Chapter 2 for a general description of the conditions necessary for growth of strains of C. sativa which are low in psychoactive
cannabinoids. It can be seen that the plant is not fastidious; indeed, the cannabis plant requires little care and attention yet under moderately intensive conditions, provides one of the longest and most versatile cellulose fibres of any plant. It has been shown that under sustainable growth conditions, on an acre for acre basis, hemp produces four times as much fibre pulp as wood (Dewey and Merill, 1916) and the yield is 200% better than cotton—a crop which requires intensive pesticide treatment to succeed.
The plant is a rapid grower, attaining a height of 10-12 feet in 12-14 weeks. Under normal conditions, the seed yield is from 12-15 bushels per acre with an average of 16-18. Twenty percent of the plant is fibre and depending on strain, growth conditions and processing, the fibre yield can be two to three times that of flax or cotton, in a range of 400-2500 pounds per acre with a mean of approximately 1000 pounds (Dewey, 1916). One acre of hemp can produce 10 dry tonnes of animal feed, including stalk and foliage; this yield may be increased with intensive fertilisation.
It has been argued by environmentalists that hemp and other products from C. sativa can be produced with a favourable environmental impact: for example, hemp requires minimal herbicides and pesticides and the plant has a very long tap root which discourages soil erosion.
As far as illicit growth of the plant is concerned, then the methods used to cultivate cannabis are as ingenious as they are devious. Clandestine, domestic cultivation operations are unearthed (and summarily dismantled by the authorities) with monotonous regularity. Sophisticated systems have been discovered only after many months of undetected operation without, apparently, knowledge of close neighbours. Because high-intensity light is a requirement, ambitious growers have resorted to the theft of sources of more or less the correct specifications from places as bizarre as 100ft up a floodlighting pylon at a soccer stadium and the external illuminations of historic buildings. Techniques for the cultivation of herbal cannabis are described elsewhere (Conrad, 1994c; Rosenthal, 1984).
This chapter does not describe the medicinal or recreational uses of Cannabis (see Chapters 1, 6-8 for this), but seeks rather to provide an overview of the plant as a contemporary source of a range of useful materials and provides some insight into the social, geo-political and economical influences which shape our attitudes to use of C. sativa in this way.
As early as 1938, the American periodical Popular Mechanics published an article entitled 'New Billion-Dollar Crop' in which it was claimed that 25,000 products could be manufactured from hemp. This may have been an imaginative over-estimate then; but in reality, the diversity of applications is stunning enough (see Table 1).
A brief description of the major uses is given below. Textiles and fine writing papers can be made from the long bast fibres. The hurds (the tougher core of the stem) can be ground down into a powder which can be used for a variety of products, including fibreboard, panelling, plywood, cavity wall insulation, packaging and even babies' nappies.
Table 1 Morden applications for C. sativa (hemp)
Table 1 Morden applications for C. sativa (hemp)
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