March 15, 1888] 



NATURE 



467 



season. I am informed by Dr. Watt that in India 

 "several other plants are treated in the same way." The 

 seeds of the several species of cultivated Guava are hard 

 and do not easily germinate. These, however, are said 

 to germinate more freely and readily when they are 

 picked up in night soil. 



While on this subject I would mention that when 

 at St. Helena in 1883 I expressed some surprise that 

 no attempt was made to utilize " urban " manure in 

 the neighbourhood of Jamestown, when the land was 

 so impoverished and yielded such poor crops. I was 

 met by the fact that if such manure was largely used 

 the land would become overrun with plants of the 

 prickly pear, Opuntia Ficiis-indica, the fruit of which 

 is largely consumed by the inhabitants. There is little 

 doubt that the seeds of this plant, like those of the 

 Guava, and I suspect also species of Passi/Iora, which 

 are swallowed whole, are capable of germination after 

 they have passed through the human body. Another 

 instance occurs to me where the use of manure has been 

 the means of distributing an undesirable plant on culti- 

 vated lands. In many tropical countries a grass known 

 as Para, Mauritius, or Scotch grass, and sometimes as 

 water grass {PufiLiiin Inirbittode), has been introduced 

 from Brazil, and highly esteemed for its rapid growth and 

 nourishing properties. It grows well in moist situations, 

 on the banks of streams, and even in soils so swampy as 

 to be suitable for nothing else. In such situations it 

 spreads rapidly and yields abundant food for cattle and 

 horses. Nothing, however, could be worse than this 

 grass for cultivated areas, where the land is required to 

 be kept free from weeds, and where crops of sugar-cane, 

 coffee, tea, and cacao are raised. It has been found that 

 where animals are fed on this grass the joints even after 

 passing through the animals have been known to grow. 

 Hence the manure, if freshly used, has been the means of 

 establishing the plant over wide areas. 



In a recent work Mr. Ball has drawn attention to 

 numerous introduced plants which are met with in South 

 America. He naturally mentions the cardoon, the wild 

 state of the common artichoke, which is now more com- 

 mon in temperate South America than it is anywhere in its 

 native home in the Mediterranean region. Darwin' doubts 

 whether any case exists on record of an invasion on so 

 grand a scale. Several hundred square miles are covered 

 with this introduced plant, which has over-run all mem- 

 bers of the aboriginal flora. The introduction of the 

 cardoon appears to have been effected directly by man 

 for the purpose of contributing to the food supply of 

 cattle ; but as regards another widely-spread plant the 

 mode of its introduction is not clearly known. 



Mr. Ball states:— "As to many of these [introduced 

 South American plants] it appears to me probable that 

 their diftusion is due more to the aid of animals than the 

 direct intervention of man. This is specially true of the 

 little immigrant which has gone farthest in colonizing 

 this part of the earth — the common stork's-bill {Erodiiun 

 cicutariuni), which has made itself equally at home in the 

 upper zone of the Peruvian Andes, in the low country of 

 Central Chili, and in the plains of North Patagonia. Its 

 extension seems to keep pace with the spread of domestic 

 animals, and as far as I have been able to ascertain it is 

 nowhere common except in districts now or formerly 

 pastured by horned cattle. It is singular that the same 

 plant should have failed to e.s.tend itself in North America, 

 being apparently confined to a few localities. It is now 

 common in the Northern Island of Nev/ Zealand, but has 

 not extended to South Africa, where two other European 

 species of the same genus are established." ^ 



Erodiiim as a genus is separated from the true Ger- 



' " Naturalist's Voyage roi nd the World," by Charles Darwin, new ed. 

 1870, p. 119. 



^ "Notes of a Naturalist in So;ith America," by John Ball, F.R.S., Lon- 

 don, i837, pp 164, 165. 



aniums amongst other reasons on account of the tails 

 of the carpels being bearded and spirally twisted on the 

 inside. It is possible that these characteristics have 

 enabled the seeds to attach themselves to the legs and 

 bodies of cattle and so effected their distribution over 

 wide areas in such situations as are favourable to their 

 growth. 



In the Island of Jamaica we have a remarkable in- 

 stance of the naturalization and wide distribution of an 

 introduced plant in the case of the Indian mango. In 

 an official Report, published in 1885, I stated that to 

 th.e mango, possibly more than any tree in the island, is 

 due the reforesting of the denuded areas in the lower 

 hills ; and as in consequence of the changes taking place 

 in the climate members of the indigenous flora are unable 

 to maintain their ground, it is fortunate the island pos- 

 sesses in a vigorous and hardy exotic like the mango the 

 means of counteracting the baneful effects of deforesta- 

 tion. It specially affects land thrown out of cultivation, 

 and the sides of roads and streams where its seeds are 

 cast aside by man and animals. It practically re-clothes 

 the hills and lower slopes with forest, and it enables the 

 land to recuperate its powers under its abundant shade- 

 giving foliage.^ It is strange that in Ceylon, which is so 

 much nearer the home of the species, the mango does 

 not spread by self-sown seedlings. This corroborates 

 Mr. Ball's statement with regard to Erodiwii cimtariuui. 

 The latter is widely spread in South America, but only 

 sparingly found in other countries under apparently 

 exactly corresponding conditions. We cannot say why 

 such anomalies exist. They do exist, however, and 

 offer problems which can only be solved by a closer study 

 of the conditions of plant life, and the interdependence 

 of plants and animals acting and reacting one upon the 

 other. 



The orange-tree was introduced to Jamaica more than 

 a hundred years ago. It is now found practically wild 

 over the settled parts of the island, and the fruit is ex- 

 ported to the value of nearly ^50,000 per annum. Up 

 to quite recently very few trees were planted. Nearly the 

 whole were sown by the agency of frugivorous birds, who 

 carried the seeds from place to place and dropped them 

 in native gardens, coffee plantations, sugar estates, and 

 grass lands. In such localities the orange-trees grew and 

 flourished, and now a demand has arisen for the fruit in 

 the United States an important industry has been estab- 

 lished, the active agents in which have been birds. The 

 agency of birds in the distribution of the seeds of plants 

 is too large a subject to be discussed at length here. A 

 valuable contribution of facts in this direction has lately 

 been made by Dr. Guppy in his important work on the 

 Solomon Islands. As the most recent addition to our 

 knowledge of what takes place in oceanic islands at the 

 present time it deserves careful attention. It will suffice 

 only to quote one or two sentences : — " Whilst through the 

 agency of the winds and currents the waves have stocked 

 the islet with its marginal vegetation, the fruit-pigeons have 

 been unconsciously stocking its interior with huge trees, 

 that have sprung from the fruits and seeds they have trans- 

 ported in their crops from the neighbouring coasts and 

 islets. The soft and often fleshy fruits on which the fruit- 

 pigeons subsist belong to numerous species of trees. 

 Some of them are as large even as a hen's &gg^ as in the 

 case of those of the species of Canariwn (' Ka-i '), which 

 have a pulpy exterior that is alone digested and retained 

 by the pigeon. Amongst other fruits and seeds on which 

 these pigeons subsist, and which they must transport from 

 one locality to another, are those of a species of Elceo- 

 carpiis ('toa'), a species of laurel {Lttsed),di nutmeg, 

 {Myristica), an Achras, one or more species of Areca 

 (palm), and probably a species (of another palm) Kentia." 



D. Morris. 



' Annu.-xl Report, Public Gardens and Plant-riins, Jamaica, for the Year 



1884, I'. 45. 



