68 5 
of Terrestrial Algae . II. 
strength before plasmolysis is to be observed in any of the cells (cf. also 
Fritsch, 1922, p. 14). To this category belong Plenrococcus Naegelii , 
Cyslococcus humicola , and under certain conditions the filamentous stage of 
Prasiola crispa} all three of which are unaffected or only very slightly 
affected by immersion in a 10 per cent, solution of sea-salt ; 2 as a matter 
of fact, to obtain decided plasmolysis in a majority of the cells, solutions 
of a strength of 20 per cent, and upwards have had to be employed. 
Not all the forms investigated, however, require solutions of such a strength 
to bring about pronounced plasmolysis. In many cases a 5 per cent, 
solution of sea-salt suffices to plasmolyse markedly many of the cells of 
Zygogoniutn ericetorum, 3 Hormidium Jlaccidum , and of the protonema of 
the moss studied. 
A second striking fact relating to the plasmolysis of these forms is the 
great inequality in the behaviour of the cells within one and the same mass 
of material, collected from the same spot and at the same time. In the case 
of the filamentous forms this is often observable within a single fila¬ 
ment ; the unplasmolysed cells are scattered singly in quite an erratic 
manner in filaments, most of whose cells are plasmolysed, and vice versa. 
In the case of the moss protonema the cells at the tips of the branches 
were very commonly, though not invariably, unaffected by the strength of 
sea-salt used (5 per cent.). By contrast with these terrestrial forms 
aquatic algae ( Spirogyra 1 Mongeotia, Oedogonium) usually exhibit a uniform 
reaction of the cells throughout whole threads, although in the case of 
Cladophora the older cells of the thick main axes are usually not plasmolysed 
by the same strength of solution as affects the cells of the finer branches. 
There is a minimum concentration of sea-salt which will produce any 
plasmolysis at all in the terrestrial forms studied, but with this strength the 
shrinkage is only very slight, and usually only to be observed in quite 
an insignificant percentage of the cells. Using solutions of progressive 
strengths above the minimum one not only observes an increase in the 
extent of plasmolysis in the individual cells, but a more or less steady 
increase in the numbers of plasmolysed cells (cf. Table I). As a general 
rule, however, it is necessary to employ strengths far above the minimum 
to bring about plasmolysis of the majority of the cells of a given mass 
of material. Thus, in the case of material of Zygogoniam ericetorump 
examined immediately after collection, the minimum concentration proved 
to be 2*25 per cent, sea-salt; even with 10 per cent, solutions, however, 
there were occasional cells that were not plasmolysed. In the case of 
1 The statement made in the first paper (Fritsch, 1922 , p. 14) that the cells of the filamentous 
stage of Prasiola are markedly plasmolysed by a 10 per cent, solution of sea-salt was probably due 
to investigation of recently inundated threads and has not been confirmed. 
2 Similar high concentrations of sugars are necessary to produce plasmolysis. Thus very few 
cells of either Pleurococcus or Prasiola plasmolyse in 40 per cent, sucrose. 
3 This is the same as the Zygnema ericetorum of the earlier paper. 
