12 Ridley .— The Distribution of Plants. 
docks is clay, which apparently does not suit it, and the sandy area, though 
not far off, is barred by buildings and river-clay deposits. 
Imperata cylindrica is also used for packing material, and is no doubt 
conveyed considerable distances in this way. I have picked up in the streets 
of Pernambuco, in Brazil, a fruiting spike of one of the African Pennisetums 
which had obviously been brought in packing for some goods from Africa. 
Besides these ways in which plants get introduced there are many other 
cases of casual introduction, and, as some of the weeds are now among the 
most widely dispersed plants in the world, it is essential, in making any 
theories on ‘ Wides ’, as they are sometimes called, to know the history of 
each species included under, this term. This requires a complete study of 
the ecology and past history of every species, so far as it is obtainable. 
I give a few illustrations of the stories of weed distribution which 
I think are very instructive. A curious history attaches to Glycosmis 
citrifolia , Lindl. ( Rutaceae), which is now apparently thoroughly established 
in St. Vincent, the Bahamas, Cuba, and French Guiana, where it appears to 
be abundant on the sandy sea-coasts. There is no other species of the genus 
occurring in the New World, all the others being confined to India, Malaya, 
and China. Griesbach, finding it apparently wild in the West Indies, actually 
described it as a new species under the name of Glycos 7 nis amcricana. 
The plant is an inconspicuous shrub with very small white flowers and 
small flesh-coloured pulpy berries, and it is neither attractive nor useful in any 
way. Its presence in the American region could never have been accounted 
for had. it not been for a note on a specimen in Kew Herbarium, which states 
that, according to Dr. Broughton, it was introduced from England in 1788 
to Jamaica under the name of the Mandarin Orange, by Henton East, Esq. 
The plant is a native of the Malay Peninsula, Java, and Hongkong, and the 
American plant agrees in all respects with the local form from Idongkong. 
Cissantpelos Pareira , Linn. (Menispermaceae), has a rather puzzling 
distribution. At one time a number of species had been made of the plant, 
but Diels, in his £ Monograph of Menispermaceae ’, has reduced them to one 
widely distributed and variable species. The plant occurs all over the 
tropics except apparently West Africa and Polynesia, is common in India, 
East Africa, and the Philippine Islands, scarce in the Malay Peninsula, and 
absent from Java. It is probably indigenous to South America. 
It was mistaken at one time for the source of the true Pareira brava of 
• * 
South America ( Chondrodendron tomentosam , Ruiz and Pavon), a drug highly 
valued by the Portuguese, and it seems very probable that the plant was 
introduced by them into the Philippines and India, as so many American 
plants were in the sixteenth century, and that it has run wild in Asia 
and Africa since. Its drupes are red and probably bird-dispersed, but that 
will not account for its wide distribution. 
Scoparia dulcis , Linn. (Scrophulariaceae), is a bushy herb or shrublet 
