H elmint ho s tacky s zeylanica. 183 
It is impossible to escape the conclusion that this metabolism is concerned 
with the elaboration of material for the growth of the exospore. That 
such material must be forthcoming is of course obvious, and the two 
sources to which one naturally looks for this supply are the spore-proto- 
plast on the one hand and the tapetum upon the other. In Helmintho - 
slachys (at least in my spirit material) the spore protoplast, after the first 
formation of the exospore, is very poor in substance, and it is very unlikely 
that it can furnish sufficient plastic material for the growth of the wall. 
When one turns to the tapetum, however, one finds here a gradual 
utilization of reserve-materials which can fully account for the substance 
which is being employed in the growth of the exospore. Moreover, if we 
deny that the tapetal material is being utilized for this purpose it is not 
easy to see what the fate of this substance may be. The growth of the 
wall of the sporangium is amply provided for by the reserve-materials 
contained in its cells, whilst the protoplasts of the spores do not increase 
in size or substance during this time, so that we are driven to associate 
the disappearance of starch and cytoplasm from the tapetum with the 
only other demonstrable utilization of material, viz., that which is adding 
to the size and thickness of the spore-coats. 
It is impossible at present, however, to decide whether the material 
elaborated in the tapetum is directly built up in the spore-walls or 
whether it first passes, in a liquid form, into the spore-protoplast which, 
either with or without further elaboration, distributes it to the walls. 
In view of the important part that the tapetal plasmodium plays in 
the growth of the spore-walls it will be necessary at this point to look 
more closely at its appearance and behaviour. We find that starch is 
abundant in the tapetal cytoplasm before the walls of the tapetum dis- 
organize and that it continues to exist there in considerable quantities 
until the period during which the exospore undergoes its most active 
growth in thickness. During this time the tapetal plasma is either very 
poor in starch or, more often, this substance is quite absent from it. When 
the exospore has completed its growth in thickness and the spore-proto- 
plast is about to add to its substance, starch can usually again be seen in 
the tapetal cytoplasm but never in quantities that can compare with those 
which occurred in the early stages of sporangial development. 
The tapetal cytoplasm at first increases somewhat in amount (im- 
mediately after the disorganization of the tapetal cells), but during the 
later history of development it slowly but steadily decreases in quantity 
(compare Figs. 18, 19, and 20). Where it abuts upon a vacuole (such as 
that which encloses a spore or spore-tetrad) the cytoplast has a very 
clearly marked plasmatic membrane ; elsewhere it is finely vacuolated in 
structure. It is the vacuolar cytoplasm which is gradually utilized in the 
metabolic processes of the plasmodium, and the plasmatic membranes, 
