88 MARGARET C. FERGUSON 



be taken by one not familiar with the history of this tissue for a 

 group of macrospore-mother-cells (fig. 168, plate XVI). In 

 fig. 148, plate XIV, the slightly reduced cytoplasm of the cells 

 of the spongy tissue and the prominence of their cell-walls are 

 sure evidences that pathological conditions have entered in, 

 though all other parts of the ovule are still perfectly normal 

 the process of disintegration having only just begun. Had 

 this ovule been left in connection with the sporophyte for a 

 longer time, the spongy tissue would undoubtedly have assumed 

 later the character shown in fig. 163. 



It is this abnormal appearance which I believe led Hofmeister 

 to conclude that there were two prothallia formed in the pines, 

 one for each season of growth. Strasburger thought that Hof- 

 meister mistook the normal spongy tissue for endosperm, and 

 Coulter and Chamberlain have recently expressed the same 

 view. Now the walls of the normal spongy tissue are never 

 thickened but remain even less prominent than those of the 

 nucellus. Hofmeister was surely too accurate a student of 

 cells as cells to have fallen into such an error. It is a well- 

 known fact that many ovules are organized in Pinus that never 

 reach maturity and they are very frequently found in the autumn 

 and late winter in the condition just described ; but with the 

 renewed growth of the healthy ovules in the spring, these fail 

 to develop farther and are soon detected by their smaller size. 

 Shortly afterward they become brown and dead. Having found 

 this thick-walled abnormal condition in the autumn and winter, 

 and in the spring finding within the ovules then developing the 

 large central cavity, it is not surprising that Hofmeister should 

 have concluded that a thick-walled transitory endosperm was 

 formed in the fall. 



The Second Period of Growth. When growth is renewed 

 in the spring the cells of the spongy tissue become organized 

 for the first time into a definite zone from two to three cells thick 

 which forms a hollow prolate spheroid immediately surrounding 

 the endosperm, and limited on its outer surface by a thin stratum 

 of disintegrating nucellar tissue. The cells and their nuclei are 

 not only somewhat larger than those of the nucellus, but their 

 most distinguishing characteristic is to be found in the greater 



