518 Piercy . — The Structure and Mode of Life of a 
when kept damp. In the case of H. flaccidum he found splitting to be 
somewhat rare under normal terrestrial conditions, but more abundant 
when growth took place in water. Borzi states that splitting sets in after 
the filaments have attained a certain length* and that dissociation into 
individual cells occurs on the advent of dryness and when the Alga is 
cultivated on gelatine. 
Klebs, 1 working with H. nitens, found that splitting depended in no 
way on the number of divisions or the length of the threads. He states 
that it is occasional, mostly occurring at points of bending, when this Alga 
is cultivated in a solution of nutritive salts under conditions favourable to 
growth, but that a lack of nutritive salts, particularly nitrogen, phosphorus, 
and magnesium salts, or a lack of moisture causes a real breaking up of the 
threads into short few-celled pieces. He observed splitting in cultures on 
pure agar-agar. Regarding the direct cause of splitting, he suggests that 
on cessation of division thickening layers are no longer added to the cuticle 
connecting two adjacent cells ; on the other hand, owing to the growth 
which goes on for some time and subsequently to the increase of turgor 
resulting from continued assimilation, the cuticle becomes stretched and 
ultimately tears. Thus the connexion between the cells is loosened here 
and there and the transverse septum then splits owing to the arching of its 
two constituent lamellae. In uniformity with Gay’s 2 observation, Klebs 
found that separation occurs more rapidly at one side of a septum than at 
the other, an angle being formed between the separating portions, while the 
filament as a whole takes on a zigzag form. « 
The process of splitting in the Woodford H or midiuni agrees with that 
outlined for other forms by Gay and Klebs. There is never a complete 
dissociation into single cells, though, under certain conditions, a small pro- 
portion of the filaments break into few-celled pieces. Usually splitting is 
rather occasional, and the fragments are of considerable length. 
The only condition which has been found effective in producing 
splitting is desiccation followed by an abundance of water. When, during 
a fortnight in summer, material kept in the greenhouse was only watered at 
intervals of two or three days, so that it became quite dry between successive 
supplies, many filaments dissociated into few-celled fragments. Other 
experiments have shown that splittings arise in material already subjected 
to desiccation for several weeks within a day or two after watering, but are 
not obvious in dry material immediately after placing it in water. Again, 
splittings were found to be common in filaments growing out of doors, which 
were examined on the second day following a spell of nine dry days. It is 
not probable that drought alone can produce splitting, as the latter did not 
appear during the desiccation experiments described below (p. 525)- 
To throw more light on the direct causes of splitting in this form of 
J l.c., p. 329 et seq. 2 1. c., p. 60. 
