Notes. 
167 
Closterium moniliferum and Cosmarium margaritif erum occur in sensible numbers. 
The Plankton of the Cam, therefore, agrees with those Thames backwaters which, 
although richer in number of individuals, still have the Diatom element predominant 
(small backwater at Walton, backwater at Shepperton J ). Yet, as I was led to 
conclude in the case of the Thames backwaters, the Plankton of the Cam is still 
rather far from resembling that of a pond, and, however different from the Plankton 
of a big stream, still shows the essential characters of a river Plankton. 
I may just add a few remarks on the Plankton of the Thames, based on three 
samples collected in April and May of this year. In correspondence with the mild- 
ness of the season, the number of individuals was already very considerable at this 
time of the year, and, as is to be expected, the green forms had reached a greater 
degree of development than at the corresponding season last year. Further, I was 
only able to recognize the Melosira-stage in one of the three samples (from Cookham), 
the other two having apparently already passed on to the Synedra- stage. It thus 
appears possible that some important changes in the periodicity of the Thames 
Plankton may take place according to the character of the season — a point which 
I hope to settle by periodical observations extending over a number of years. 
University College, London. 
September 28, 1904. 
F. E. FRITSCH. 
ON A BRILLIANT PIGMENT APPEARING AFTER INJURY IN SPECIES 
OF JACOBINIA (N. O. ACANTHACEAE). — (Abstract.) 2 — Shoots of certain species 
of Jacobinia 3 , when bruised and extracted with water, yield a beautiful purplish liquid. 
Liebmann discovered these species while travelling in Central America about half a 
century ago, and found the Indians using them for dyeing purposes. Thomas 4 , while in 
Mexico, submitted the colouring principle of Jacobinia Mohintli to a brief examination. 
Since then these plants seem tohave received no further investigation, and their peculiarity 
is apparently little known to botanists. The object of the present paper is to direct 
attention to this conspicuous example of pigment-formation, and to give a few details 
concerning the chromogen and the colouring matter resulting from it. The author 
hopes to make a full investigation later. So far, the observations have been made on 
the two very similar species, Jacobinia tindoria and Jacobinia Mohintli. The peculiar 
behaviour of the former plant was brought to the writer’s notice, when in Ceylon, by 
Mr. Willis, the Director of the Royal Botanic Gardens, Peradeniya. 
The pigment does not exist as such in the living plant, but appears only on 
death. Leaves, however, killed by boiling water remain green and do not darken. 
Hence the pigment most likely arises through enzymic action. Slight alkalinity 
hastens its appearance. Oxygen is also necessary for its formation. It is readily 
soluble in water and gives a fluorescent solution, purple to violet by transmitted and 
blood-red by reflected light. A trace of acid robs the solution of most of its colour. 
The original tint reappears on neutralization. Alkali turns it bluer, and if strong 
1 Cf. Fritsch, Further observations, &c., pp. 639-646. 
2 Read before the Botanical Section of the British Association, Cambridge, August, 1904. 
3 Jacobinia tinctoria, J. Mohintli, J . incana,J. neglecta , and /. verrucosa. 
4 Journ. de Pharm. et de Chimie, 1866, ser. iv. t. iii. p. 251. 
