Such poisonous orders should of course be avoided, but much more dangerous are those deadly plants which appear as it were accidentally in orders which are amongst the most useful friends of man. Amongst the grasses there is the deadly Darnel (Lolium temulentum), a first cousin and not very unlike the very commonest and one of the most useful grasses—Rye Grass (Lolium perenne).
Then in the useful Carrot order, there are such dangerous and even deadly plants as Fool's Parsley, Water Dropwort, and Cowbane. Œnanthe crocata (Water Dropwort) is one of the very commonest marsh and ditch plants in Great Britain. It is perfectly well known to botanists as distinctly poisonous, yet in 1902 a veterinary surgeon brought me some of the tuberous roots to name, and told me that six fine young cows were lying dead on a neighbouring farm through having eaten them!
A particularly useful order of plants (Leguminosæ), the Beans and Peas, contains a few poisonous species. It is said that in every year children are sure to be killed by eating the seeds of the Laburnum, and to this order belong also the Calabar Bean and Crab's Eyes. The last named is only fatal when introduced below the skin in small quantities. The seeds of the Bitter Vetch (Lathyrus sativus) produce paralysis of the legs in man and also in horses. The Crazy or Loco weed of North America is sometimes eaten by horses in the Western United States. The wretched animals stagger about as if intoxicated, and eventually die. Belonging to this same order is the Wild Tamarind, or Jumbai, of Jamaica (Leucæna glauca). It is a weedy-looking acacia, and extremely common in all tropical countries. Dr. D. Morris thus alludes to it:—[109]
"Mr. Robert Russell, of St. Ann's, informs me that horses feeding on the leaves of this plant completely lose the hair from their manes and tails. This ... statement was supported by the testimony of so many people acquainted with the facts that there was no reason to doubt it. Many years afterwards (in December, 1895), I renewed my acquaintance with the plant in the Bahamas. The plant was much more plentiful there than in Jamaica; it was, in fact, distinctly encouraged in the former islands as a fodder plant. The people were fully aware of the singular effect it produced on horses, and added that it also affected mules and donkeys. Its effect on pigs was still more marked. These animals assumed a completely naked condition, and appeared without a single hair on their body. Horses badly affected by Jumbai were occasionally seen in the streets of Nassau, where they were known as 'cigar-tails.' Such depilated animals, although apparently healthy, were considerably depreciated in value. They were said to recover when fed exclusively on corn and grass. The new hair was, however, of a different colour and texture, 'so the animals were never quite the same.' One animal was cited as having lost its hoofs as well, and in consequence it had to be kept in slings until they grew again and hardened. The effects of the Jumbai on horses, mules, donkeys, and pigs were regarded as accidental—due to neglect or ignorance. The plant was really encouraged to supply food for cattle, sheep, and goats. The latter greedily devoured it and were not perceptibly affected by it. It will be noticed that the animals affected were non-ruminants, while those not affected were ruminants. The probable explanation is that the ruminants, by thoroughly mixing the food with saliva and slowly digesting it, were enabled to neutralize the action of the poison and escape injury. The seeds probably contain the deleterious principle in a greater degree than any other part of the plant. It was a common experience that animals introduced from other localities suffered more than the native animals. The latter were either immune or had learnt to avoid the plant as noxious to them."
That animals resident in a district are not poisoned by plants which are often fatal to sheep and cattle when on the march through it, has been often observed in Australia. The great "mobs" or droves of sheep passing slowly on their travels through the bush to a new district are often poisoned by the Caustic Creeper (Euphorbia Drummondi). "The head swells to an enormous extent, becoming so heavy that the animal cannot support it, and drags it along the ground"; but this does not apparently happen to resident cattle. Similarly for the Darling Pea or Indigo (Swainsonia galegifolia). At one place this was growing abundantly where some travelling horses were hobbled for the night. "They had been on the road some nine weeks, and were up to this date caught without any difficulty. On this occasion ... their eyes were staring out of their heads, and they were prancing against trees and shrubs.... When driven they would suddenly stop, turn round and round, and keep throwing their heads up as if they had been hit under the jaw.... Two out of nine died, and five others had to be left at the camp."[110]
In other natural orders we find one or two dangerous plants amongst a whole series of perfectly harmless or useful forms. The Oleander, in the Olive order, Corncockle (Lychnis floscuculli), in the Pink order, Lactuca Scariola amongst Compositæ and others are all cases in point. So also is the Yew amongst Coniferæ, etc.
How do animals recognize these particular plants as being dangerous whilst all their allies are harmless? But the reader will answer that they do not; it is well known that animals are killed by eating poisonous plants, therefore poison cannot possibly be any protection against animals.
This is one of those interesting questions in which the suppression of apparently irrelevant details produces confusion.
As a matter of fact, wild animals, or even domesticated animals in nearly a wild state, do not eat the poisonous plants of the country in which they and their forefathers have been brought up—that is provided that they are either adult or are accompanied by full-grown animals. Almost every case of cattle-poisoning in Great Britain occurs when young calves, foals, or lambs are turned loose in the fields without any mature older head amongst them. Sometimes valuable stable-bred animals are lost, especially by eating yew-leaves, but there are exceedingly few instances of full-grown cattle being caught in such foolishness. When cattle, horses, or sheep are turned loose in a new country, plenty of cases do occur, and it is possible that they might make mistakes with unknown foreign plants which had escaped into their pastures here.
But almost every case of poisoning, even of cattle, shows that it is young cattle who foolishly eat foxgloves, dropwort, buttercup, etc., and occasionally die thereby.