668 TRANSACTIONS OF SECTION K. 
phyllin, both monocarboxylic acids. The reaction consists initially of 
hydrolysis and subsequently in the main of elimination of carbon dioxide. 
So long as chlorophyll itself was not known in the pure state my method 
of working consisted in treatment of crude chlorophyll solutions with 
alkali to determine what acids take away from chlorophyll, and the 
investigation of the products of the action of acids to ascertain what part 
of the molecule of the pigment is destroyed by alkalis. 
Gentle warming with acids led to the discovery of those constituents 
of chlorophyll—about 30 per cent. in all—which are lost during alkaline 
hydrolysis. Chlorophyll contains an aliphatic alcohol of high molecular 
weight, viz., phytol, C..H,,O. This is unsaturated, and therefore autoxidis- 
able. Its presence causes chlorophyll to be a wax. Phytol appears 
to be present in practically constant quantity in the chlorophyll from plants 
of all orders, yet it is not an essential component of chlorophyll. 
In the course of the comparative analysis of the chlorophyll of different 
plants, for which about 100 species have provisionally served, a few excep- 
tions to the normal composition have been observed. All these exceptions 
occur in species of Labiate and Solunaceew. In these exceptions chloro- 
phyll contains no phytol, and accordingly it can be made to crystallise. 
It has the composition C,,H,,0,N, Mg, gives six per cent. magnesium oxide 
on ignition, and contains no phosphorus or iron. This crystalline chloro- 
phyll is an ester containing two molecules of alcohol; amorphous 
chlorophyll contains one molecule of phytol and one of alcohol. 
The pure chlorophyll obtained crystalline from Galeopsis, Lamium, 
Stachys, &c., appears to be the same as crystals observed under the micro- 
scope by Borodie in St. Petersburg in 1881. In opposition to Borodie, 
however, the author considers that the crystalline variety of chlorophyll 
is relatively rare. Many Labiates and Solanacee contain the crystalline, 
others the amorphous, phytol-yielding variety of chlorophyll. Crystalline 
chlorophyll is adapted to the quantitative estimation of chlorophyll by 
colorimetric methods in leaves and plant extracts: it varies between a half and 
one per cent. of the dried leaf. The foregoing cbservations were in many 
tases made on material from dried leaves. It is probable that during 
drying, &c., the chlorophyll has already undergone change. Such considera- 
tions, without affecting what has been already discovered, promise further 
discoveries when fresh plants are investigated. 
2. The Fundamental Causes of Succession among Plant Associations. 
By Professor Hanry C. Cow ss. 
In the early days of ecological geography little was attempted except 
the description of the various sorts of plant associations, much as the 
early taxonomists and morphologists were content to cease their labours 
when they had described the materials under investigation. At present 
no taxonomic or morphologic treatise is complete unless the facts presented 
are related in some way to evolution; the investigation of kinship has 
replaced the mere collation of unrelated facts. 
During the past decade some ecologists have endeavoured to work out 
the genetic relationships existing among plant associations, and to many 
of us it has seemed that the first step is the study of the life histories of 
these associations in each region. In this respect we have been but following 
in the well-beaten track that has been made by morphologists and 
taxonomists along the trail blazed by Darwin in 1859. Just as evolution 
has knit together into a genetic whole the previously isolated phenomena 
of plant structure, so the evolutionary study of plant associations has 
shown that what have been regarded as separate entities are often merely 
‘tages in development. It has been shown that plant associations are 
