86 



1. The rate and mode of growth of the leaf 

 and flower stalks. 



The growth of the leaves and their stalks begins late in spring, and 

 that of the flowers only in July. The quick rate of growth of both leaf 

 and flower stalks is a very conspicuous example of longitudinal growth 

 (Langenwachsthum). The most vigorous increase seems to take place in 

 July and the beginning of August. Though my observations began some- 

 what later, I found many young shoots coming above the water from time 

 to time, and easily got good materials for observation in plants growing 

 near the brink of the pond, where the water-level was about 20-30 c. m. 

 above the mud, and the rhizome about 30-40 c. m. deep down in it. 



The measurements taken were lengths above the water-level, using 

 the milimeter measuring-rule. To estimate differences in the rate of growth 

 in different part of the stalk and to distinguish the more vigorously grow- 

 ing part from that which was slower in growth or no longer growing, 

 markings were made in various parts of the stalk, with Japanese carbon- 

 ink (called "sunn," in Japanese). The marking with carbon was not only 

 for comparing the relative growth of various parts in the same stalk, 

 but also for making clear the non-growing part, for exclusion from the 

 measurement, thus making the measurement error smaller than it would 

 have been, had the measuring begun at the water-level. Thus having a 

 fiexd point in the non-growing part of the stalk, I could easily correct the 

 changes of the water-level, which was found to undulate within 2-3 c. m. 

 in the pond. My observations began at noon of 12th August and con- 

 tinued about two weeks. The daily measurements were made at noon, 

 except on the first five days when the observations were taken between 

 one and three o'clock in the afternoon. 



The young leaf, when it has just emerged from the water, is tightly 

 closed, having somewhat the shape of a cigar pointed at both ends and 

 in a vertical position and connected at the middle of its length with 

 the end of comparatively long stalk. As the stalk grows upwards the 

 cigar-formed leaf-hud grows longitudinally and gradually deviates from 

 the vertical position until it approaches a horizontal one, then unclosing at 

 both sides of the median line, into a nearly circular disc. The flower-bud 

 which is situated at the apex of the flower stalk is very small when it 

 first conies out of the water, but it grows in size and height as its stalk 

 grows in length. 



