EMBRYOGENY OF Ptnus Pinaster. 55 



embryo doimiwards, but it would be a natural consequence that the 

 embryo would be in close contact with the prothallus cells below 

 them, and that the latter would be somewhat crushed. It is found 

 on the contrary that there is an empty space surrounding, and 

 especially in front of, the embryo, as shown in figures i, 4, 5, 8, 9, 11. 



The only cases where crushing of the prothallus cells had clearly 

 taken place were after the cotyledons had appeared, and would 

 probably be due to a very rapid elongation of the tissues at this time. 

 Even this has not been seen in Pinus itself, but in Callitris, and a mic- 

 rophoto of it will be published later in connection with a study of 

 that genus. 



It is noticeable that in stages considerably before the differentia- 

 tion of the cotyledons a definite region of the prothalAis, surround- 

 ing tf e embryos, is devoid of starch, and this at on' e suggests the 

 presence of an enzyme, such as diastase, secreted by the embryos. 



A series of experiments was carried out during January ,1909, 

 when abundance of material was available, in the hope of obtaining 

 positive evidence on this piont. The prothalli containing young 

 embryos were crushed in water, the extract filtered and tested very 

 carefully for diastase. The tests were carried out at four tempera- 

 tures and extended over a period of about four days, during which 

 time no trace of sugar was formed from the starch used, nor was 

 any trace of sugar (either cane or invert sugar) to be found in the 

 extract. 



This proves conclusively that the enzyme presumed to be present 

 is not diastase, but the writer ventures the opinion that some 

 enzyme of a rather unstable nature, and capable of dissolving both 

 starch and cellulose, must be secreted by the em.bryo cells of Pinus. 

 This seems the only possible explanation of the space surrounding 

 the embrvo. bounded by disorganising, but not crushed, cells 

 and nuclei. 



Figures i, 2, 5, 6 represent the most usual sequence of events 

 met with in early stages, the four emybro ceils remaining connectod 

 and each dividing by a transverse wall, followed by a second trans- 

 verse wall in the apical cell. This order is, however, b}' no means 

 constant. Figure 3 shows a case in which two suspensors had 

 become free from one another a good deal sooner than is usual. In 

 one of these two embrj-os the second division was b}' a vertical wall 

 in the proximal cell. Coulter and Cfiam.berlain (') mention cases 

 in Pinus laricio where the first wall in the embryo cell is vertical. 

 No such case has been met with in Pinus pinaster, nor does the 

 distal cell in these early stages ever divide by a vertical wall. 

 Nevertheless the increase in length of the young embryo is brought 

 about almost entirely by the activity of the distal cell, at first by 

 transverse divisions (fi.gure 4) and later probably by oblique divi- 

 sions. The latter point is inferred from sequences similar to that 

 shown in figures 8-10 (note especially figure 9). An obliquely 

 placed spindle has not actually been seen, so that it may be only 

 that the appearance of an apical cell is simulated, an opinion ex- 

 pressed b}' Coulter (4). In any case there can be no doubt that in 

 the youngest stages (up to the age of the embryos of figure 8) a 

 true iunctional apical cell is present, corresponding to each suspensor 



