1899] DEVELOPMENT OF THE MICROSPORANGIUM 351 
plate stage, so that it was impossible to determine just what 
happened to them at this point. The daughter chromosomes 
_ move to the poles very evenly, that is, with the same degree of 
tapidity (fig. 38). A count here showed the seven segments 
present. Although the daughter nuclei are quite small, the 
chromosomes remain distinct for some time, and can be again 
counted. After a time the nucleolar bodies also reappear, and 
the division is then complete. 
THE MICROSPORE. 
Our knowledge of the internal structure of the pollen grain 
_teally dates from the time of Hartig.? In this author’s work is 
the first mention of the discovery in Tradescantia and several 
other plants of two nuclei in the pollen. This important dis- 
every seems not to have been noticed by subsequent investi- 
fators until Strasburger’s exhaustive work appeared in 1877.73 
twas not until then that the fact was generally recognized that 
Wo nuclei are to be found sooner or later in the development of 
‘very angiospermous microspore. This author was also able to 
‘emonstrate that the larger of these two nuclei is to be con- 
‘dered as a vegetative or prothallial nucleus and the smaller a 
| eacrative nucleus.** Strasburger found also that a second 
tivision takes place regularly in angiosperms, either in the spore 
"Self or in the pollen tube just before fertilization. Two sperm 
_ bells ada thus formed from the one generative cell. 
& Since that time many investigators working upon widely 
ferent Plants have found two nuclei, and these observations 
_ fad to one result, namely the confirmation of Strasburger’s 
ations in every essential particular. The time of forma- 
"2, ultimate Shape of the generative cell, and the time when 
latter divides were indeed not always the same in different 
“ats; on the contrary, all degrees of variation were found, 
om of Which are noted below. 
5 ag Untersuchungen aus der physiologische Lab. Land. Lehrung. Ber- 
* Sarsten 3: 294. 1866. 
Befruchtung und Zellth 
Befry 
y 
« : eilung 18, 1877. f 
entungs Vorginge bei den Phanerogamen 5, 1884. 
